Explicitly add python-numpy dependency to install-build-deps.

[chromium-blink-merge.git] / tools / auto_bisect / bisect_perf_regression.py

#!/usr/bin/env python
# Copyright (c) 2013 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Performance Test Bisect Tool

This script bisects a series of changelists using binary search. It starts at
a bad revision where a performance metric has regressed, and asks for a last
known-good revision. It will then binary search across this revision range by
syncing, building, and running a performance test. If the change is
suspected to occur as a result of WebKit/V8 changes, the script will
further bisect changes to those depots and attempt to narrow down the revision
range.

Example usage using SVN revisions:

./tools/bisect_perf_regression.py -c\
  "out/Release/performance_ui_tests --gtest_filter=ShutdownTest.SimpleUserQuit"\
  -g 168222 -b 168232 -m shutdown/simple-user-quit

Be aware that if you're using the git workflow and specify an SVN revision,
the script will attempt to find the git SHA1 where SVN changes up to that
revision were merged in.

Example usage using git hashes:

./tools/bisect_perf_regression.py -c\
  "out/Release/performance_ui_tests --gtest_filter=ShutdownTest.SimpleUserQuit"\
  -g 1f6e67861535121c5c819c16a666f2436c207e7b\
  -b b732f23b4f81c382db0b23b9035f3dadc7d925bb\
  -m shutdown/simple-user-quit
"""

import copy
import errno
import hashlib
import logging
import argparse
import os
import re
import shlex
import shutil
import StringIO
import sys
import time
import zipfile

sys.path.append(os.path.join(
    os.path.dirname(__file__), os.path.pardir, 'telemetry'))

from bisect_printer import BisectPrinter
from bisect_results import BisectResults
from bisect_state import BisectState
import bisect_utils
import builder
import query_crbug
import math_utils
import request_build
import source_control
from telemetry.util import cloud_storage

# The script is in chromium/src/tools/auto_bisect. Throughout this script,
# we use paths to other things in the chromium/src repository.

# Possible return values from BisectPerformanceMetrics.RunTest.
BUILD_RESULT_SUCCEED = 0
BUILD_RESULT_FAIL = 1
BUILD_RESULT_SKIPPED = 2

# Maximum time in seconds to wait after posting build request to the try server.
# TODO: Change these values based on the actual time taken by buildbots on
# the try server.
MAX_MAC_BUILD_TIME = 14400
MAX_WIN_BUILD_TIME = 14400
MAX_LINUX_BUILD_TIME = 14400

# The confidence percentage we require to consider the initial range a
# regression based on the test results of the inital good and bad revisions.
REGRESSION_CONFIDENCE = 95

# Patch template to add a new file, DEPS.sha under src folder.
# This file contains SHA1 value of the DEPS changes made while bisecting
# dependency repositories. This patch send along with DEPS patch to try server.
# When a build requested is posted with a patch, bisect builders on try server,
# once build is produced, it reads SHA value from this file and appends it
# to build archive filename.
DEPS_SHA_PATCH = """diff --git DEPS.sha DEPS.sha
new file mode 100644
--- /dev/null
+++ DEPS.sha
@@ -0,0 +1 @@
+%(deps_sha)s
"""

REGRESSION_CONFIDENCE_ERROR_TEMPLATE = """
We could not reproduce the regression with this test/metric/platform combination
with enough confidence.

Here are the results for the given "good" and "bad" revisions:
"Good" revision: {good_rev}
\tMean: {good_mean}
\tStandard error: {good_std_err}
\tSample size: {good_sample_size}

"Bad" revision: {bad_rev}
\tMean: {bad_mean}
\tStandard error: {bad_std_err}
\tSample size: {bad_sample_size}

NOTE: There's still a chance that this is actually a regression, but you may
      need to bisect a different platform."""

# Git branch name used to run bisect try jobs.
BISECT_TRYJOB_BRANCH = 'bisect-tryjob'
# Git master branch name.
BISECT_MASTER_BRANCH = 'master'
# File to store 'git diff' content.
BISECT_PATCH_FILE = 'deps_patch.txt'
# SVN repo where the bisect try jobs are submitted.
SVN_REPO_URL = 'svn://svn.chromium.org/chrome-try/try-perf'

class RunGitError(Exception):

  def __str__(self):
    return '%s\nError executing git command.' % self.args[0]


def GetSHA1HexDigest(contents):
  """Returns SHA1 hex digest of the given string."""
  return hashlib.sha1(contents).hexdigest()


def GetZipFileName(build_revision=None, target_arch='ia32', patch_sha=None):
  """Gets the archive file name for the given revision."""
  def PlatformName():
    """Return a string to be used in paths for the platform."""
    if bisect_utils.IsWindowsHost():
      # Build archive for x64 is still stored with the "win32" suffix.
      # See chromium_utils.PlatformName().
      if bisect_utils.Is64BitWindows() and target_arch == 'x64':
        return 'win32'
      return 'win32'
    if bisect_utils.IsLinuxHost():
      # Android builds are also archived with the "full-build-linux prefix.
      return 'linux'
    if bisect_utils.IsMacHost():
      return 'mac'
    raise NotImplementedError('Unknown platform "%s".' % sys.platform)

  base_name = 'full-build-%s' % PlatformName()
  if not build_revision:
    return base_name
  if patch_sha:
    build_revision = '%s_%s' % (build_revision, patch_sha)
  return '%s_%s.zip' % (base_name, build_revision)


def GetRemoteBuildPath(build_revision, target_platform='chromium',
                       target_arch='ia32', patch_sha=None):
  """Returns the URL to download the build from."""
  def GetGSRootFolderName(target_platform):
    """Returns the Google Cloud Storage root folder name."""
    if bisect_utils.IsWindowsHost():
      if bisect_utils.Is64BitWindows() and target_arch == 'x64':
        return 'Win x64 Builder'
      return 'Win Builder'
    if bisect_utils.IsLinuxHost():
      if target_platform == 'android':
        return 'android_perf_rel'
      return 'Linux Builder'
    if bisect_utils.IsMacHost():
      return 'Mac Builder'
    raise NotImplementedError('Unsupported Platform "%s".' % sys.platform)

  base_filename = GetZipFileName(
      build_revision, target_arch, patch_sha)
  builder_folder = GetGSRootFolderName(target_platform)
  return '%s/%s' % (builder_folder, base_filename)


def FetchFromCloudStorage(bucket_name, source_path, destination_path):
  """Fetches file(s) from the Google Cloud Storage.

  Args:
    bucket_name: Google Storage bucket name.
    source_path: Source file path.
    destination_path: Destination file path.

  Returns:
    Downloaded file path if exists, otherwise None.
  """
  target_file = os.path.join(destination_path, os.path.basename(source_path))
  try:
    if cloud_storage.Exists(bucket_name, source_path):
      logging.info('Fetching file from gs//%s/%s ...',
                   bucket_name, source_path)
      cloud_storage.Get(bucket_name, source_path, destination_path)
      if os.path.exists(target_file):
        return target_file
    else:
      logging.info('File gs://%s/%s not found in cloud storage.',
                    bucket_name, source_path)
  except Exception as e:
    logging.warn('Something went wrong while fetching file from cloud: %s', e)
    if os.path.exists(target_file):
      os.remove(target_file)
  return None


# This was copied from build/scripts/common/chromium_utils.py.
def ExtractZip(filename, output_dir, verbose=True):
  """ Extract the zip archive in the output directory."""
  MaybeMakeDirectory(output_dir)

  # On Linux and Mac, we use the unzip command as it will
  # handle links and file bits (executable), which is much
  # easier then trying to do that with ZipInfo options.
  #
  # The Mac Version of unzip unfortunately does not support Zip64, whereas
  # the python module does, so we have to fall back to the python zip module
  # on Mac if the file size is greater than 4GB.
  #
  # On Windows, try to use 7z if it is installed, otherwise fall back to python
  # zip module and pray we don't have files larger than 512MB to unzip.
  unzip_cmd = None
  if ((bisect_utils.IsMacHost()
       and os.path.getsize(filename) < 4 * 1024 * 1024 * 1024)
      or bisect_utils.IsLinuxHost()):
    unzip_cmd = ['unzip', '-o']
  elif (bisect_utils.IsWindowsHost()
        and os.path.exists('C:\\Program Files\\7-Zip\\7z.exe')):
    unzip_cmd = ['C:\\Program Files\\7-Zip\\7z.exe', 'x', '-y']

  if unzip_cmd:
    # Make sure path is absolute before changing directories.
    filepath = os.path.abspath(filename)
    saved_dir = os.getcwd()
    os.chdir(output_dir)
    command = unzip_cmd + [filepath]
    result = bisect_utils.RunProcess(command)
    os.chdir(saved_dir)
    if result:
      raise IOError('unzip failed: %s => %s' % (str(command), result))
  else:
    assert bisect_utils.IsWindowsHost() or bisect_utils.IsMacHost()
    zf = zipfile.ZipFile(filename)
    for name in zf.namelist():
      if verbose:
        logging.info('Extracting %s', name)
      zf.extract(name, output_dir)
      if bisect_utils.IsMacHost():
        # Restore permission bits.
        os.chmod(os.path.join(output_dir, name),
                 zf.getinfo(name).external_attr >> 16L)


def WriteStringToFile(text, file_name):
  """Writes text to a file, raising an RuntimeError on failure."""
  try:
    with open(file_name, 'wb') as f:
      f.write(text)
  except IOError:
    raise RuntimeError('Error writing to file [%s]' % file_name)


def ReadStringFromFile(file_name):
  """Writes text to a file, raising an RuntimeError on failure."""
  try:
    with open(file_name) as f:
      return f.read()
  except IOError:
    raise RuntimeError('Error reading file [%s]' % file_name)


def ChangeBackslashToSlashInPatch(diff_text):
  """Formats file paths in the given patch text to Unix-style paths."""
  if not diff_text:
    return None
  diff_lines = diff_text.split('\n')
  for i in range(len(diff_lines)):
    line = diff_lines[i]
    if line.startswith('--- ') or line.startswith('+++ '):
      diff_lines[i] = line.replace('\\', '/')
  return '\n'.join(diff_lines)


def _ParseRevisionsFromDEPSFileManually(deps_file_contents):
  """Parses the vars section of the DEPS file using regular expressions.

  Args:
    deps_file_contents: The DEPS file contents as a string.

  Returns:
    A dictionary in the format {depot: revision} if successful, otherwise None.
  """
  # We'll parse the "vars" section of the DEPS file.
  rxp = re.compile('vars = {(?P<vars_body>[^}]+)', re.MULTILINE)
  re_results = rxp.search(deps_file_contents)

  if not re_results:
    return None

  # We should be left with a series of entries in the vars component of
  # the DEPS file with the following format:
  # 'depot_name': 'revision',
  vars_body = re_results.group('vars_body')
  rxp = re.compile(r"'(?P<depot_body>[\w_-]+)':[\s]+'(?P<rev_body>[\w@]+)'",
                   re.MULTILINE)
  re_results = rxp.findall(vars_body)

  return dict(re_results)


def _WaitUntilBuildIsReady(
    fetch_build, bot_name, builder_host, builder_port, build_request_id,
    max_timeout):
  """Waits until build is produced by bisect builder on try server.

  Args:
    fetch_build: Function to check and download build from cloud storage.
    bot_name: Builder bot name on try server.
    builder_host Try server host name.
    builder_port: Try server port.
    build_request_id: A unique ID of the build request posted to try server.
    max_timeout: Maximum time to wait for the build.

  Returns:
     Downloaded archive file path if exists, otherwise None.
  """
  # Build number on the try server.
  build_num = None
  # Interval to check build on cloud storage.
  poll_interval = 60
  # Interval to check build status on try server in seconds.
  status_check_interval = 600
  last_status_check = time.time()
  start_time = time.time()
  while True:
    # Checks for build on gs://chrome-perf and download if exists.
    res = fetch_build()
    if res:
      return (res, 'Build successfully found')
    elapsed_status_check = time.time() - last_status_check
    # To avoid overloading try server with status check requests, we check
    # build status for every 10 minutes.
    if elapsed_status_check > status_check_interval:
      last_status_check = time.time()
      if not build_num:
        # Get the build number on try server for the current build.
        build_num = request_build.GetBuildNumFromBuilder(
            build_request_id, bot_name, builder_host, builder_port)
      # Check the status of build using the build number.
      # Note: Build is treated as PENDING if build number is not found
      # on the the try server.
      build_status, status_link = request_build.GetBuildStatus(
          build_num, bot_name, builder_host, builder_port)
      if build_status == request_build.FAILED:
        return (None, 'Failed to produce build, log: %s' % status_link)
    elapsed_time = time.time() - start_time
    if elapsed_time > max_timeout:
      return (None, 'Timed out: %ss without build' % max_timeout)

    logging.info('Time elapsed: %ss without build.', elapsed_time)
    time.sleep(poll_interval)
    # For some reason, mac bisect bots were not flushing stdout periodically.
    # As a result buildbot command is timed-out. Flush stdout on all platforms
    # while waiting for build.
    sys.stdout.flush()


def _UpdateV8Branch(deps_content):
  """Updates V8 branch in DEPS file to process v8_bleeding_edge.

  Check for "v8_branch" in DEPS file if exists update its value
  with v8_bleeding_edge branch. Note: "v8_branch" is added to DEPS
  variable from DEPS revision 254916, therefore check for "src/v8":
  <v8 source path> in DEPS in order to support prior DEPS revisions
  and update it.

  Args:
    deps_content: DEPS file contents to be modified.

  Returns:
    Modified DEPS file contents as a string.
  """
  new_branch = r'branches/bleeding_edge'
  v8_branch_pattern = re.compile(r'(?<="v8_branch": ")(.*)(?=")')
  if re.search(v8_branch_pattern, deps_content):
    deps_content = re.sub(v8_branch_pattern, new_branch, deps_content)
  else:
    # Replaces the branch assigned to "src/v8" key in DEPS file.
    # Format of "src/v8" in DEPS:
    # "src/v8":
    #    (Var("googlecode_url") % "v8") + "/trunk@" + Var("v8_revision"),
    # So, "/trunk@" is replace with "/branches/bleeding_edge@"
    v8_src_pattern = re.compile(
        r'(?<="v8"\) \+ "/)(.*)(?=@" \+ Var\("v8_revision"\))', re.MULTILINE)
    if re.search(v8_src_pattern, deps_content):
      deps_content = re.sub(v8_src_pattern, new_branch, deps_content)
  return deps_content


def _UpdateDEPSForAngle(revision, depot, deps_file):
  """Updates DEPS file with new revision for Angle repository.

  This is a hack for Angle depot case because, in DEPS file "vars" dictionary
  variable contains "angle_revision" key that holds git hash instead of
  SVN revision.

  And sometimes "angle_revision" key is not specified in "vars" variable,
  in such cases check "deps" dictionary variable that matches
  angle.git@[a-fA-F0-9]{40}$ and replace git hash.
  """
  deps_var = bisect_utils.DEPOT_DEPS_NAME[depot]['deps_var']
  try:
    deps_contents = ReadStringFromFile(deps_file)
    # Check whether the depot and revision pattern in DEPS file vars variable
    # e.g. "angle_revision": "fa63e947cb3eccf463648d21a05d5002c9b8adfa".
    angle_rev_pattern = re.compile(r'(?<="%s": ")([a-fA-F0-9]{40})(?=")' %
                                   deps_var, re.MULTILINE)
    match = re.search(angle_rev_pattern, deps_contents)
    if match:
      # Update the revision information for the given depot
      new_data = re.sub(angle_rev_pattern, revision, deps_contents)
    else:
      # Check whether the depot and revision pattern in DEPS file deps
      # variable. e.g.,
      # "src/third_party/angle": Var("chromium_git") +
      # "/angle/angle.git@fa63e947cb3eccf463648d21a05d5002c9b8adfa",.
      angle_rev_pattern = re.compile(
          r'(?<=angle\.git@)([a-fA-F0-9]{40})(?=")', re.MULTILINE)
      match = re.search(angle_rev_pattern, deps_contents)
      if not match:
        logging.info('Could not find angle revision information in DEPS file.')
        return False
      new_data = re.sub(angle_rev_pattern, revision, deps_contents)
    # Write changes to DEPS file
    WriteStringToFile(new_data, deps_file)
    return True
  except IOError, e:
    logging.warn('Something went wrong while updating DEPS file, %s', e)
  return False


def _TryParseHistogramValuesFromOutput(metric, text):
  """Attempts to parse a metric in the format HISTOGRAM <graph: <trace>.

  Args:
    metric: The metric as a list of [<trace>, <value>] strings.
    text: The text to parse the metric values from.

  Returns:
    A list of floating point numbers found, [] if none were found.
  """
  metric_formatted = 'HISTOGRAM %s: %s= ' % (metric[0], metric[1])

  text_lines = text.split('\n')
  values_list = []

  for current_line in text_lines:
    if metric_formatted in current_line:
      current_line = current_line[len(metric_formatted):]

      try:
        histogram_values = eval(current_line)

        for b in histogram_values['buckets']:
          average_for_bucket = float(b['high'] + b['low']) * 0.5
          # Extends the list with N-elements with the average for that bucket.
          values_list.extend([average_for_bucket] * b['count'])
      except Exception:
        pass

  return values_list


def _TryParseResultValuesFromOutput(metric, text):
  """Attempts to parse a metric in the format RESULT <graph>: <trace>= ...

  Args:
    metric: The metric as a list of [<trace>, <value>] string pairs.
    text: The text to parse the metric values from.

  Returns:
    A list of floating point numbers found.
  """
  # Format is: RESULT <graph>: <trace>= <value> <units>
  metric_re = re.escape('RESULT %s: %s=' % (metric[0], metric[1]))

  # The log will be parsed looking for format:
  # <*>RESULT <graph_name>: <trace_name>= <value>
  single_result_re = re.compile(
      metric_re + r'\s*(?P<VALUE>[-]?\d*(\.\d*)?)')

  # The log will be parsed looking for format:
  # <*>RESULT <graph_name>: <trace_name>= [<value>,value,value,...]
  multi_results_re = re.compile(
      metric_re + r'\s*\[\s*(?P<VALUES>[-]?[\d\., ]+)\s*\]')

  # The log will be parsed looking for format:
  # <*>RESULT <graph_name>: <trace_name>= {<mean>, <std deviation>}
  mean_stddev_re = re.compile(
      metric_re +
      r'\s*\{\s*(?P<MEAN>[-]?\d*(\.\d*)?),\s*(?P<STDDEV>\d+(\.\d*)?)\s*\}')

  text_lines = text.split('\n')
  values_list = []
  for current_line in text_lines:
    # Parse the output from the performance test for the metric we're
    # interested in.
    single_result_match = single_result_re.search(current_line)
    multi_results_match = multi_results_re.search(current_line)
    mean_stddev_match = mean_stddev_re.search(current_line)
    if (not single_result_match is None and
        single_result_match.group('VALUE')):
      values_list += [single_result_match.group('VALUE')]
    elif (not multi_results_match is None and
          multi_results_match.group('VALUES')):
      metric_values = multi_results_match.group('VALUES')
      values_list += metric_values.split(',')
    elif (not mean_stddev_match is None and
          mean_stddev_match.group('MEAN')):
      values_list += [mean_stddev_match.group('MEAN')]

  values_list = [float(v) for v in values_list
                 if bisect_utils.IsStringFloat(v)]

  # If the metric is times/t, we need to sum the timings in order to get
  # similar regression results as the try-bots.
  metrics_to_sum = [
      ['times', 't'],
      ['times', 'page_load_time'],
      ['cold_times', 'page_load_time'],
      ['warm_times', 'page_load_time'],
  ]

  if metric in metrics_to_sum:
    if values_list:
      values_list = [reduce(lambda x, y: float(x) + float(y), values_list)]

  return values_list


def _ParseMetricValuesFromOutput(metric, text):
  """Parses output from performance_ui_tests and retrieves the results for
  a given metric.

  Args:
    metric: The metric as a list of [<trace>, <value>] strings.
    text: The text to parse the metric values from.

  Returns:
    A list of floating point numbers found.
  """
  metric_values = _TryParseResultValuesFromOutput(metric, text)

  if not metric_values:
    metric_values = _TryParseHistogramValuesFromOutput(metric, text)

  return metric_values


def _GenerateProfileIfNecessary(command_args):
  """Checks the command line of the performance test for dependencies on
  profile generation, and runs tools/perf/generate_profile as necessary.

  Args:
    command_args: Command line being passed to performance test, as a list.

  Returns:
    False if profile generation was necessary and failed, otherwise True.
  """
  if '--profile-dir' in ' '.join(command_args):
    # If we were using python 2.7+, we could just use the argparse
    # module's parse_known_args to grab --profile-dir. Since some of the
    # bots still run 2.6, have to grab the arguments manually.
    arg_dict = {}
    args_to_parse = ['--profile-dir', '--browser']

    for arg_to_parse in args_to_parse:
      for i, current_arg in enumerate(command_args):
        if arg_to_parse in current_arg:
          current_arg_split = current_arg.split('=')

          # Check 2 cases, --arg=<val> and --arg <val>
          if len(current_arg_split) == 2:
            arg_dict[arg_to_parse] = current_arg_split[1]
          elif i + 1 < len(command_args):
            arg_dict[arg_to_parse] = command_args[i+1]

    path_to_generate = os.path.join('tools', 'perf', 'generate_profile')

    if arg_dict.has_key('--profile-dir') and arg_dict.has_key('--browser'):
      profile_path, profile_type = os.path.split(arg_dict['--profile-dir'])
      return not bisect_utils.RunProcess(['python', path_to_generate,
          '--profile-type-to-generate', profile_type,
          '--browser', arg_dict['--browser'], '--output-dir', profile_path])
    return False
  return True


def _CheckRegressionConfidenceError(
    good_revision,
    bad_revision,
    known_good_value,
    known_bad_value):
  """Checks whether we can be confident beyond a certain degree that the given
  metrics represent a regression.

  Args:
    good_revision: string representing the commit considered 'good'
    bad_revision: Same as above for 'bad'.
    known_good_value: A dict with at least: 'values', 'mean' and 'std_err'
    known_bad_value: Same as above.

  Returns:
    False if there is no error (i.e. we can be confident there's a regressioni),
    a string containing the details of the lack of confidence otherwise.
  """
  error = False
  # Adding good and bad values to a parameter list.
  confidenceParams = []
  for l in [known_bad_value['values'], known_good_value['values']]:
    # Flatten if needed
    if isinstance(l, list) and all([isinstance(x, list) for x in l]):
      confidenceParams.append(sum(l, []))
    else:
      confidenceParams.append(l)
  regression_confidence = BisectResults.ConfidenceScore(*confidenceParams)
  if regression_confidence < REGRESSION_CONFIDENCE:
    error = REGRESSION_CONFIDENCE_ERROR_TEMPLATE.format(
        good_rev=good_revision,
        good_mean=known_good_value['mean'],
        good_std_err=known_good_value['std_err'],
        good_sample_size=len(known_good_value['values']),
        bad_rev=bad_revision,
        bad_mean=known_bad_value['mean'],
        bad_std_err=known_bad_value['std_err'],
        bad_sample_size=len(known_bad_value['values']))
  return error

class DepotDirectoryRegistry(object):

  def __init__(self, src_cwd):
    self.depot_cwd = {}
    for depot in bisect_utils.DEPOT_NAMES:
      # The working directory of each depot is just the path to the depot, but
      # since we're already in 'src', we can skip that part.
      path_in_src = bisect_utils.DEPOT_DEPS_NAME[depot]['src'][4:]
      self.SetDepotDir(depot, os.path.join(src_cwd, path_in_src))

    self.SetDepotDir('chromium', src_cwd)

  def SetDepotDir(self, depot_name, depot_dir):
    self.depot_cwd[depot_name] = depot_dir

  def GetDepotDir(self, depot_name):
    if depot_name in self.depot_cwd:
      return self.depot_cwd[depot_name]
    else:
      assert False, ('Unknown depot [ %s ] encountered. Possibly a new one '
                     'was added without proper support?' % depot_name)

  def ChangeToDepotDir(self, depot_name):
    """Given a depot, changes to the appropriate working directory.

    Args:
      depot_name: The name of the depot (see DEPOT_NAMES).
    """
    os.chdir(self.GetDepotDir(depot_name))

def _PrepareBisectBranch(parent_branch, new_branch):
  """Creates a new branch to submit bisect try job.

  Args:
    parent_branch: Parent branch to be used to create new branch.
    new_branch: New branch name.
  """
  current_branch, returncode = bisect_utils.RunGit(
      ['rev-parse', '--abbrev-ref', 'HEAD'])
  if returncode:
    raise RunGitError('Must be in a git repository to send changes to trybots.')

  current_branch = current_branch.strip()
  # Make sure current branch is master.
  if current_branch != parent_branch:
    output, returncode = bisect_utils.RunGit(['checkout', '-f', parent_branch])
    if returncode:
      raise RunGitError('Failed to checkout branch: %s.' % output)

  # Delete new branch if exists.
  output, returncode = bisect_utils.RunGit(['branch', '--list'])
  if new_branch in output:
    output, returncode = bisect_utils.RunGit(['branch', '-D', new_branch])
    if returncode:
      raise RunGitError('Deleting branch failed, %s', output)

  # Check if the tree is dirty: make sure the index is up to date and then
  # run diff-index.
  bisect_utils.RunGit(['update-index', '--refresh', '-q'])
  output, returncode = bisect_utils.RunGit(['diff-index', 'HEAD'])
  if output:
    raise RunGitError('Cannot send a try job with a dirty tree.')

  # Create/check out the telemetry-tryjob branch, and edit the configs
  # for the tryjob there.
  output, returncode = bisect_utils.RunGit(['checkout', '-b', new_branch])
  if returncode:
    raise RunGitError('Failed to checkout branch: %s.' % output)

  output, returncode = bisect_utils.RunGit(
      ['branch', '--set-upstream-to', parent_branch])
  if returncode:
    raise RunGitError('Error in git branch --set-upstream-to')


def _BuilderTryjob(git_revision, bot_name, bisect_job_name, patch=None):
  """Attempts to run a tryjob from the current directory.

  Args:
    git_revision: A Git hash revision.
    bot_name: Name of the bisect bot to be used for try job.
    bisect_job_name: Bisect try job name.
    patch: A DEPS patch (used while bisecting 3rd party repositories).
  """
  try:
    # Temporary branch for running tryjob.
    _PrepareBisectBranch(BISECT_MASTER_BRANCH, BISECT_TRYJOB_BRANCH)
    patch_content = '/dev/null'
    # Create a temporary patch file, if it fails raise an exception.
    if patch:
      WriteStringToFile(patch, BISECT_PATCH_FILE)
      patch_content = BISECT_PATCH_FILE

    try_cmd = ['try',
               '-b', bot_name,
               '-r', git_revision,
               '-n', bisect_job_name,
               '--svn_repo=%s' % SVN_REPO_URL,
               '--diff=%s' % patch_content
              ]
    # Execute try job to build revision.
    output, returncode = bisect_utils.RunGit(try_cmd)

    if returncode:
      raise RunGitError('Could not execute tryjob: %s.\n Error: %s' % (
                         'git %s' % ' '.join(try_cmd), output))
    logging.info('Try job successfully submitted.\n TryJob Details: %s\n%s',
           'git %s' % ' '.join(try_cmd), output)
  finally:
    # Delete patch file if exists
    try:
      os.remove(BISECT_PATCH_FILE)
    except OSError as e:
      if e.errno != errno.ENOENT:
        raise
    # Checkout master branch and delete bisect-tryjob branch.
    bisect_utils.RunGit(['checkout', '-f', BISECT_MASTER_BRANCH])
    bisect_utils.RunGit(['branch', '-D', BISECT_TRYJOB_BRANCH])


class BisectPerformanceMetrics(object):
  """This class contains functionality to perform a bisection of a range of
  revisions to narrow down where performance regressions may have occurred.

  The main entry-point is the Run method.
  """

  def __init__(self, opts, src_cwd):
    """Constructs a BisectPerformancesMetrics object.

    Args:
      opts: BisectOptions object containing parsed options.
      src_cwd: Root src/ directory of the test repository (inside bisect/ dir).
    """
    super(BisectPerformanceMetrics, self).__init__()

    self.opts = opts
    self.src_cwd = src_cwd
    self.depot_registry = DepotDirectoryRegistry(self.src_cwd)
    self.printer = BisectPrinter(self.opts, self.depot_registry)
    self.cleanup_commands = []
    self.warnings = []
    self.builder = builder.Builder.FromOpts(opts)

  def PerformCleanup(self):
    """Performs cleanup when script is finished."""
    os.chdir(self.src_cwd)
    for c in self.cleanup_commands:
      if c[0] == 'mv':
        shutil.move(c[1], c[2])
      else:
        assert False, 'Invalid cleanup command.'

  def GetRevisionList(self, depot, bad_revision, good_revision):
    """Retrieves a list of all the commits between the bad revision and
    last known good revision."""

    cwd = self.depot_registry.GetDepotDir(depot)
    return source_control.GetRevisionList(bad_revision, good_revision, cwd=cwd)

  def _ParseRevisionsFromDEPSFile(self, depot):
    """Parses the local DEPS file to determine blink/skia/v8 revisions which may
    be needed if the bisect recurses into those depots later.

    Args:
      depot: Name of depot being bisected.

    Returns:
      A dict in the format {depot:revision} if successful, otherwise None.
    """
    try:
      deps_data = {
          'Var': lambda _: deps_data["vars"][_],
          'From': lambda *args: None,
      }

      deps_file = bisect_utils.FILE_DEPS_GIT
      if not os.path.exists(deps_file):
        deps_file = bisect_utils.FILE_DEPS
      execfile(deps_file, {}, deps_data)
      deps_data = deps_data['deps']

      rxp = re.compile(".git@(?P<revision>[a-fA-F0-9]+)")
      results = {}
      for depot_name, depot_data in bisect_utils.DEPOT_DEPS_NAME.iteritems():
        if (depot_data.get('platform') and
            depot_data.get('platform') != os.name):
          continue

        if depot_data.get('recurse') and depot in depot_data.get('from'):
          depot_data_src = depot_data.get('src') or depot_data.get('src_old')
          src_dir = deps_data.get(depot_data_src)
          if src_dir:
            self.depot_registry.SetDepotDir(depot_name, os.path.join(
                self.src_cwd, depot_data_src[4:]))
            re_results = rxp.search(src_dir)
            if re_results:
              results[depot_name] = re_results.group('revision')
            else:
              warning_text = ('Could not parse revision for %s while bisecting '
                              '%s' % (depot_name, depot))
              if not warning_text in self.warnings:
                self.warnings.append(warning_text)
          else:
            results[depot_name] = None
      return results
    except ImportError:
      deps_file_contents = ReadStringFromFile(deps_file)
      parse_results = _ParseRevisionsFromDEPSFileManually(deps_file_contents)
      results = {}
      for depot_name, depot_revision in parse_results.iteritems():
        depot_revision = depot_revision.strip('@')
        logging.warn(depot_name, depot_revision)
        for cur_name, cur_data in bisect_utils.DEPOT_DEPS_NAME.iteritems():
          if (cur_data.has_key('deps_var') and
              cur_data['deps_var'] == depot_name):
            src_name = cur_name
            results[src_name] = depot_revision
            break
      return results

  def _Get3rdPartyRevisions(self, depot):
    """Parses the DEPS file to determine WebKit/v8/etc... versions.

    Args:
      depot: A depot name. Should be in the DEPOT_NAMES list.

    Returns:
      A dict in the format {depot: revision} if successful, otherwise None.
    """
    cwd = os.getcwd()
    self.depot_registry.ChangeToDepotDir(depot)

    results = {}

    if depot == 'chromium' or depot == 'android-chrome':
      results = self._ParseRevisionsFromDEPSFile(depot)
      os.chdir(cwd)

    if depot == 'v8':
      # We can't try to map the trunk revision to bleeding edge yet, because
      # we don't know which direction to try to search in. Have to wait until
      # the bisect has narrowed the results down to 2 v8 rolls.
      results['v8_bleeding_edge'] = None

    return results

  def BackupOrRestoreOutputDirectory(self, restore=False, build_type='Release'):
    """Backs up or restores build output directory based on restore argument.

    Args:
      restore: Indicates whether to restore or backup. Default is False(Backup)
      build_type: Target build type ('Release', 'Debug', 'Release_x64' etc.)

    Returns:
      Path to backup or restored location as string. otherwise None if it fails.
    """
    build_dir = os.path.abspath(
        builder.GetBuildOutputDirectory(self.opts, self.src_cwd))
    source_dir = os.path.join(build_dir, build_type)
    destination_dir = os.path.join(build_dir, '%s.bak' % build_type)
    if restore:
      source_dir, destination_dir = destination_dir, source_dir
    if os.path.exists(source_dir):
      RemoveDirectoryTree(destination_dir)
      shutil.move(source_dir, destination_dir)
      return destination_dir
    return None

  def _GetBuildArchiveForRevision(self, revision, gs_bucket, target_arch,
                                  patch_sha, out_dir):
    """Checks and downloads build archive for a given revision.

    Checks for build archive with Git hash or SVN revision. If either of the
    file exists, then downloads the archive file.

    Args:
      revision: A git commit hash.
      gs_bucket: Cloud storage bucket name.
      target_arch: Architecture name string, e.g. "ia32" or "x64".
      patch_sha: A SHA1 hex digest of a DEPS file patch, used while
          bisecting 3rd party repositories.
      out_dir: Build output directory where downloaded file is stored.

    Returns:
      Downloaded archive file path if exists, otherwise None.
    """
    # Source archive file path on cloud storage using Git revision.
    source_file = GetRemoteBuildPath(
        revision, self.opts.target_platform, target_arch, patch_sha)
    downloaded_archive = FetchFromCloudStorage(gs_bucket, source_file, out_dir)
    if not downloaded_archive:
      # Get commit position for the given SHA.
      commit_position = source_control.GetCommitPosition(revision)
      if commit_position:
        # Source archive file path on cloud storage using SVN revision.
        source_file = GetRemoteBuildPath(
            commit_position, self.opts.target_platform, target_arch, patch_sha)
        return FetchFromCloudStorage(gs_bucket, source_file, out_dir)
    return downloaded_archive

  def _DownloadAndUnzipBuild(self, revision, depot, build_type='Release'):
    """Downloads the build archive for the given revision.

    Args:
      revision: The git revision to download.
      depot: The name of a dependency repository. Should be in DEPOT_NAMES.
      build_type: Target build type, e.g. Release', 'Debug', 'Release_x64' etc.

    Returns:
      True if download succeeds, otherwise False.
    """
    patch = None
    patch_sha = None
    if depot != 'chromium':
      # Create a DEPS patch with new revision for dependency repository.
      revision, patch = self.CreateDEPSPatch(depot, revision)

    if patch:
      # Get the SHA of the DEPS changes patch.
      patch_sha = GetSHA1HexDigest(patch)

      # Update the DEPS changes patch with a patch to create a new file named
      # 'DEPS.sha' and add patch_sha evaluated above to it.
      patch = '%s\n%s' % (patch, DEPS_SHA_PATCH % {'deps_sha': patch_sha})

    build_dir = builder.GetBuildOutputDirectory(self.opts, self.src_cwd)
    downloaded_file = self._WaitForBuildDownload(
        revision, build_dir, deps_patch=patch, deps_patch_sha=patch_sha)
    if not downloaded_file:
      return False
    return self._UnzipAndMoveBuildProducts(downloaded_file, build_dir,
                                           build_type=build_type)

  def _WaitForBuildDownload(self, revision, build_dir, deps_patch=None,
                            deps_patch_sha=None):
    """Tries to download a zip archive for a build.

    This involves seeing whether the archive is already available, and if not,
    then requesting a build and waiting before downloading.

    Args:
      revision: A git commit hash.
      build_dir: The directory to download the build into.
      deps_patch: A patch which changes a dependency repository revision in
          the DEPS, if applicable.
      deps_patch_sha: The SHA1 hex digest of the above patch.

    Returns:
      File path of the downloaded file if successful, otherwise None.
    """
    abs_build_dir = os.path.abspath(build_dir)
    fetch_build_func = lambda: self._GetBuildArchiveForRevision(
        revision, self.opts.gs_bucket, self.opts.target_arch,
        deps_patch_sha, abs_build_dir)

    # Downloaded archive file path, downloads build archive for given revision.
    # This will be False if the build isn't yet available.
    downloaded_file = fetch_build_func()

    # When build archive doesn't exist, post a build request to try server
    # and wait for the build to be produced.
    if not downloaded_file:
      downloaded_file = self._RequestBuildAndWait(
          revision, fetch_build=fetch_build_func, patch=deps_patch)
      if not downloaded_file:
        return None

    return downloaded_file

  def _RequestBuildAndWait(self, git_revision, fetch_build, patch=None):
    """Triggers a try job for a build job.

    This function prepares and starts a try job on the tryserver.chromium.perf
    master, and waits for the binaries to be produced and archived in cloud
    storage. Once the build is ready it's downloaded.

    Args:
      git_revision: A Git hash revision.
      fetch_build: Function to check and download build from cloud storage.
      patch: A DEPS patch (used while bisecting 3rd party repositories).

    Returns:
      Downloaded archive file path when requested build exists and download is
      successful, otherwise None.
    """
    if not fetch_build:
      return False

    # Create a unique ID for each build request posted to try server builders.
    # This ID is added to "Reason" property of the build.
    build_request_id = GetSHA1HexDigest(
        '%s-%s-%s' % (git_revision, patch, time.time()))

    # Reverts any changes to DEPS file.
    source_control.CheckoutFileAtRevision(
      bisect_utils.FILE_DEPS, git_revision, cwd=self.src_cwd)

    bot_name = self._GetBuilderName(self.opts.target_platform)
    build_timeout = self._GetBuilderBuildTime()
    target_file = None
    try:
      # Execute try job request to build revision with patch.
      _BuilderTryjob(git_revision, bot_name, build_request_id, patch)
      target_file, error_msg = _WaitUntilBuildIsReady(
          fetch_build, bot_name, self.opts.builder_host,
          self.opts.builder_port, build_request_id, build_timeout)
      if not target_file:
        logging.warn('%s [revision: %s]', error_msg, git_revision)
    except RunGitError as e:
      logging.warn('Failed to post builder try job for revision: [%s].\n'
             'Error: %s', git_revision, e)

    return target_file

  @staticmethod
  def _GetBuilderName(target_platform):
    """Gets builder bot name and build time in seconds based on platform."""
    if bisect_utils.IsWindowsHost():
      return 'win_perf_bisect_builder'
    if bisect_utils.IsLinuxHost():
      if target_platform == 'android':
        return 'android_perf_bisect_builder'
      return 'linux_perf_bisect_builder'
    if bisect_utils.IsMacHost():
      return 'mac_perf_bisect_builder'
    raise NotImplementedError('Unsupported Platform "%s".' % sys.platform)

  @staticmethod
  def _GetBuilderBuildTime():
    """Returns the time to wait for a build after requesting one."""
    if bisect_utils.IsWindowsHost():
      return MAX_WIN_BUILD_TIME
    if bisect_utils.IsLinuxHost():
      return MAX_LINUX_BUILD_TIME
    if bisect_utils.IsMacHost():
      return MAX_MAC_BUILD_TIME
    raise NotImplementedError('Unsupported Platform "%s".' % sys.platform)

  def _UnzipAndMoveBuildProducts(self, downloaded_file, build_dir,
                                 build_type='Release'):
    """Unzips the build archive and moves it to the build output directory.

    The build output directory is whereever the binaries are expected to
    be in order to start Chrome and run tests.

    Args:
      downloaded_file: File path of the downloaded zip file.
      build_dir: Directory where the the zip file was downloaded to.
      build_type: "Release" or "Debug".

    Returns:
      True if successful, False otherwise.
    """
    abs_build_dir = os.path.abspath(build_dir)
    output_dir = os.path.join(
        abs_build_dir, GetZipFileName(target_arch=self.opts.target_arch))

    try:
      RemoveDirectoryTree(output_dir)
      self.BackupOrRestoreOutputDirectory(restore=False)
      # Build output directory based on target(e.g. out/Release, out/Debug).
      target_build_output_dir = os.path.join(abs_build_dir, build_type)
      ExtractZip(downloaded_file, abs_build_dir)
      if not os.path.exists(output_dir):
        # Due to recipe changes, the builds extract folder contains
        # out/Release instead of full-build-<platform>/Release.
        if os.path.exists(os.path.join(abs_build_dir, 'out', build_type)):
          output_dir = os.path.join(abs_build_dir, 'out', build_type)
        else:
          raise IOError('Missing extracted folder %s ' % output_dir)

      logging.info('Moving build from %s to %s',
                   output_dir, target_build_output_dir)
      shutil.move(output_dir, target_build_output_dir)
      return True
    except Exception as e:
      logging.info('Something went wrong while extracting archive file: %s', e)
      self.BackupOrRestoreOutputDirectory(restore=True)
      # Cleanup any leftovers from unzipping.
      if os.path.exists(output_dir):
        RemoveDirectoryTree(output_dir)
    finally:
      # Delete downloaded archive
      if os.path.exists(downloaded_file):
        os.remove(downloaded_file)
    return False

  def IsDownloadable(self, depot):
    """Checks if build can be downloaded based on target platform and depot."""
    if (self.opts.target_platform in ['chromium', 'android'] and
        self.opts.gs_bucket):
      return (depot == 'chromium' or
              'chromium' in bisect_utils.DEPOT_DEPS_NAME[depot]['from'] or
              'v8' in bisect_utils.DEPOT_DEPS_NAME[depot]['from'])
    return False

  def UpdateDepsContents(self, deps_contents, depot, git_revision, deps_key):
    """Returns modified version of DEPS file contents.

    Args:
      deps_contents: DEPS file content.
      depot: Current depot being bisected.
      git_revision: A git hash to be updated in DEPS.
      deps_key: Key in vars section of DEPS file to be searched.

    Returns:
      Updated DEPS content as string if deps key is found, otherwise None.
    """
    # Check whether the depot and revision pattern in DEPS file vars
    # e.g. for webkit the format is "webkit_revision": "12345".
    deps_revision = re.compile(r'(?<="%s": ")([0-9]+)(?=")' % deps_key,
                               re.MULTILINE)
    new_data = None
    if re.search(deps_revision, deps_contents):
      commit_position = source_control.GetCommitPosition(
          git_revision, self.depot_registry.GetDepotDir(depot))
      if not commit_position:
        logging.warn('Could not determine commit position for %s', git_revision)
        return None
      # Update the revision information for the given depot
      new_data = re.sub(deps_revision, str(commit_position), deps_contents)
    else:
      # Check whether the depot and revision pattern in DEPS file vars
      # e.g. for webkit the format is "webkit_revision": "559a6d4ab7a84c539..".
      deps_revision = re.compile(
          r'(?<=["\']%s["\']: ["\'])([a-fA-F0-9]{40})(?=["\'])' % deps_key,
          re.MULTILINE)
      if re.search(deps_revision, deps_contents):
        new_data = re.sub(deps_revision, git_revision, deps_contents)
    if new_data:
      # For v8_bleeding_edge revisions change V8 branch in order
      # to fetch bleeding edge revision.
      if depot == 'v8_bleeding_edge':
        new_data = _UpdateV8Branch(new_data)
        if not new_data:
          return None
    return new_data

  def UpdateDeps(self, revision, depot, deps_file):
    """Updates DEPS file with new revision of dependency repository.

    This method search DEPS for a particular pattern in which depot revision
    is specified (e.g "webkit_revision": "123456"). If a match is found then
    it resolves the given git hash to SVN revision and replace it in DEPS file.

    Args:
      revision: A git hash revision of the dependency repository.
      depot: Current depot being bisected.
      deps_file: Path to DEPS file.

    Returns:
      True if DEPS file is modified successfully, otherwise False.
    """
    if not os.path.exists(deps_file):
      return False

    deps_var = bisect_utils.DEPOT_DEPS_NAME[depot]['deps_var']
    # Don't update DEPS file if deps_var is not set in DEPOT_DEPS_NAME.
    if not deps_var:
      logging.warn('DEPS update not supported for Depot: %s', depot)
      return False

    # Hack for Angle repository. In the DEPS file, "vars" dictionary variable
    # contains "angle_revision" key that holds git hash instead of SVN revision.
    # And sometime "angle_revision" key is not specified in "vars" variable.
    # In such cases check, "deps" dictionary variable that matches
    # angle.git@[a-fA-F0-9]{40}$ and replace git hash.
    if depot == 'angle':
      return _UpdateDEPSForAngle(revision, depot, deps_file)

    try:
      deps_contents = ReadStringFromFile(deps_file)
      updated_deps_content = self.UpdateDepsContents(
          deps_contents, depot, revision, deps_var)
      # Write changes to DEPS file
      if updated_deps_content:
        WriteStringToFile(updated_deps_content, deps_file)
        return True
    except IOError, e:
      logging.warn('Something went wrong while updating DEPS file. [%s]', e)
    return False

  def CreateDEPSPatch(self, depot, revision):
    """Modifies DEPS and returns diff as text.

    Args:
      depot: Current depot being bisected.
      revision: A git hash revision of the dependency repository.

    Returns:
      A tuple with git hash of chromium revision and DEPS patch text.
    """
    deps_file_path = os.path.join(self.src_cwd, bisect_utils.FILE_DEPS)
    if not os.path.exists(deps_file_path):
      raise RuntimeError('DEPS file does not exists.[%s]' % deps_file_path)
    # Get current chromium revision (git hash).
    cmd = ['rev-parse', 'HEAD']
    chromium_sha = bisect_utils.CheckRunGit(cmd).strip()
    if not chromium_sha:
      raise RuntimeError('Failed to determine Chromium revision for %s' %
                         revision)
    if ('chromium' in bisect_utils.DEPOT_DEPS_NAME[depot]['from'] or
        'v8' in bisect_utils.DEPOT_DEPS_NAME[depot]['from']):
      # Checkout DEPS file for the current chromium revision.
      if source_control.CheckoutFileAtRevision(
          bisect_utils.FILE_DEPS, chromium_sha, cwd=self.src_cwd):
        if self.UpdateDeps(revision, depot, deps_file_path):
          diff_command = [
              'diff',
              '--src-prefix=',
              '--dst-prefix=',
              '--no-ext-diff',
               bisect_utils.FILE_DEPS,
          ]
          diff_text = bisect_utils.CheckRunGit(diff_command, cwd=self.src_cwd)
          return (chromium_sha, ChangeBackslashToSlashInPatch(diff_text))
        else:
          raise RuntimeError(
              'Failed to update DEPS file for chromium: [%s]' % chromium_sha)
      else:
        raise RuntimeError(
            'DEPS checkout Failed for chromium revision : [%s]' % chromium_sha)
    return (None, None)

  def ObtainBuild(self, depot, revision=None):
    """Obtains a build by either downloading or building directly.

    Args:
      depot: Dependency repository name.
      revision: A git commit hash. If None is given, the currently checked-out
          revision is built.

    Returns:
      True for success.
    """
    if self.opts.debug_ignore_build:
      return True

    build_success = False
    cwd = os.getcwd()
    os.chdir(self.src_cwd)
    # Fetch build archive for the given revision from the cloud storage when
    # the storage bucket is passed.
    if self.IsDownloadable(depot) and revision:
      build_success = self._DownloadAndUnzipBuild(revision, depot)
    else:
      # These codes are executed when bisect bots builds binaries locally.
      build_success = self.builder.Build(depot, self.opts)
    os.chdir(cwd)
    return build_success

  def RunGClientHooks(self):
    """Runs gclient with runhooks command.

    Returns:
      True if gclient reports no errors.
    """
    if self.opts.debug_ignore_build:
      return True
    return not bisect_utils.RunGClient(['runhooks'], cwd=self.src_cwd)

  def _IsBisectModeUsingMetric(self):
    return self.opts.bisect_mode in [bisect_utils.BISECT_MODE_MEAN,
                                     bisect_utils.BISECT_MODE_STD_DEV]

  def _IsBisectModeReturnCode(self):
    return self.opts.bisect_mode in [bisect_utils.BISECT_MODE_RETURN_CODE]

  def _IsBisectModeStandardDeviation(self):
    return self.opts.bisect_mode in [bisect_utils.BISECT_MODE_STD_DEV]

  def GetCompatibleCommand(self, command_to_run, revision, depot):
    """Return a possibly modified test command depending on the revision.

    Prior to crrev.com/274857 *only* android-chromium-testshell
    Then until crrev.com/276628 *both* (android-chromium-testshell and
    android-chrome-shell) work. After that rev 276628 *only*
    android-chrome-shell works. The bisect_perf_regression.py script should
    handle these cases and set appropriate browser type based on revision.
    """
    if self.opts.target_platform in ['android']:
      # When its a third_party depot, get the chromium revision.
      if depot != 'chromium':
        revision = bisect_utils.CheckRunGit(
            ['rev-parse', 'HEAD'], cwd=self.src_cwd).strip()
      commit_position = source_control.GetCommitPosition(revision,
                                                         cwd=self.src_cwd)
      if not commit_position:
        return command_to_run
      cmd_re = re.compile(r'--browser=(?P<browser_type>\S+)')
      matches = cmd_re.search(command_to_run)
      if bisect_utils.IsStringInt(commit_position) and matches:
        cmd_browser = matches.group('browser_type')
        if commit_position <= 274857 and cmd_browser == 'android-chrome-shell':
          return command_to_run.replace(cmd_browser,
                                        'android-chromium-testshell')
        elif (commit_position >= 276628 and
              cmd_browser == 'android-chromium-testshell'):
          return command_to_run.replace(cmd_browser,
                                        'android-chrome-shell')
    return command_to_run

  def RunPerformanceTestAndParseResults(
      self, command_to_run, metric, reset_on_first_run=False,
      upload_on_last_run=False, results_label=None):
    """Runs a performance test on the current revision and parses the results.

    Args:
      command_to_run: The command to be run to execute the performance test.
      metric: The metric to parse out from the results of the performance test.
          This is the result chart name and trace name, separated by slash.
          May be None for perf try jobs.
      reset_on_first_run: If True, pass the flag --reset-results on first run.
      upload_on_last_run: If True, pass the flag --upload-results on last run.
      results_label: A value for the option flag --results-label.
          The arguments reset_on_first_run, upload_on_last_run and results_label
          are all ignored if the test is not a Telemetry test.

    Returns:
      (values dict, 0) if --debug_ignore_perf_test was passed.
      (values dict, 0, test output) if the test was run successfully.
      (error message, -1) if the test couldn't be run.
      (error message, -1, test output) if the test ran but there was an error.
    """
    success_code, failure_code = 0, -1

    if self.opts.debug_ignore_perf_test:
      fake_results = {
          'mean': 0.0,
          'std_err': 0.0,
          'std_dev': 0.0,
          'values': [0.0]
      }

      # When debug_fake_test_mean is set, its value is returned as the mean
      # and the flag is cleared so that further calls behave as if it wasn't
      # set (returning the fake_results dict as defined above).
      if self.opts.debug_fake_first_test_mean:
        fake_results['mean'] = float(self.opts.debug_fake_first_test_mean)
        self.opts.debug_fake_first_test_mean = 0

      return (fake_results, success_code)

    # For Windows platform set posix=False, to parse windows paths correctly.
    # On Windows, path separators '\' or '\\' are replace by '' when posix=True,
    # refer to http://bugs.python.org/issue1724822. By default posix=True.
    args = shlex.split(command_to_run, posix=not bisect_utils.IsWindowsHost())

    if not _GenerateProfileIfNecessary(args):
      err_text = 'Failed to generate profile for performance test.'
      return (err_text, failure_code)

    is_telemetry = bisect_utils.IsTelemetryCommand(command_to_run)

    start_time = time.time()

    metric_values = []
    output_of_all_runs = ''
    for i in xrange(self.opts.repeat_test_count):
      # Can ignore the return code since if the tests fail, it won't return 0.
      current_args = copy.copy(args)
      if is_telemetry:
        if i == 0 and reset_on_first_run:
          current_args.append('--reset-results')
        if i == self.opts.repeat_test_count - 1 and upload_on_last_run:
          current_args.append('--upload-results')
        if results_label:
          current_args.append('--results-label=%s' % results_label)
      try:
        output, return_code = bisect_utils.RunProcessAndRetrieveOutput(
            current_args, cwd=self.src_cwd)
      except OSError, e:
        if e.errno == errno.ENOENT:
          err_text = ('Something went wrong running the performance test. '
                      'Please review the command line:\n\n')
          if 'src/' in ' '.join(args):
            err_text += ('Check that you haven\'t accidentally specified a '
                         'path with src/ in the command.\n\n')
          err_text += ' '.join(args)
          err_text += '\n'

          return (err_text, failure_code)
        raise

      output_of_all_runs += output
      if self.opts.output_buildbot_annotations:
        print output

      if metric and self._IsBisectModeUsingMetric():
        metric_values += _ParseMetricValuesFromOutput(metric, output)
        # If we're bisecting on a metric (ie, changes in the mean or
        # standard deviation) and no metric values are produced, bail out.
        if not metric_values:
          break
      elif self._IsBisectModeReturnCode():
        metric_values.append(return_code)

      elapsed_minutes = (time.time() - start_time) / 60.0
      if elapsed_minutes >= self.opts.max_time_minutes:
        break

    if metric and len(metric_values) == 0:
      err_text = 'Metric %s was not found in the test output.' % metric
      # TODO(qyearsley): Consider also getting and displaying a list of metrics
      # that were found in the output here.
      return (err_text, failure_code, output_of_all_runs)

    # If we're bisecting on return codes, we're really just looking for zero vs
    # non-zero.
    values = {}
    if self._IsBisectModeReturnCode():
      # If any of the return codes is non-zero, output 1.
      overall_return_code = 0 if (
          all(current_value == 0 for current_value in metric_values)) else 1

      values = {
          'mean': overall_return_code,
          'std_err': 0.0,
          'std_dev': 0.0,
          'values': metric_values,
      }

      print 'Results of performance test: Command returned with %d' % (
          overall_return_code)
      print
    elif metric:
      # Need to get the average value if there were multiple values.
      truncated_mean = math_utils.TruncatedMean(
          metric_values, self.opts.truncate_percent)
      standard_err = math_utils.StandardError(metric_values)
      standard_dev = math_utils.StandardDeviation(metric_values)

      if self._IsBisectModeStandardDeviation():
        metric_values = [standard_dev]

      values = {
          'mean': truncated_mean,
          'std_err': standard_err,
          'std_dev': standard_dev,
          'values': metric_values,
      }

      print 'Results of performance test: %12f %12f' % (
          truncated_mean, standard_err)
      print
    return (values, success_code, output_of_all_runs)

  def PerformPreBuildCleanup(self):
    """Performs cleanup between runs."""
    print 'Cleaning up between runs.'
    print

    # Leaving these .pyc files around between runs may disrupt some perf tests.
    for (path, _, files) in os.walk(self.src_cwd):
      for cur_file in files:
        if cur_file.endswith('.pyc'):
          path_to_file = os.path.join(path, cur_file)
          os.remove(path_to_file)

  def _RunPostSync(self, _depot):
    """Performs any work after syncing.

    Args:
      depot: Depot name.

    Returns:
      True if successful.
    """
    if self.opts.target_platform == 'android':
      if not builder.SetupAndroidBuildEnvironment(self.opts,
          path_to_src=self.src_cwd):
        return False

    return self.RunGClientHooks()

  @staticmethod
  def ShouldSkipRevision(depot, revision):
    """Checks whether a particular revision can be safely skipped.

    Some commits can be safely skipped (such as a DEPS roll), since the tool
    is git based those changes would have no effect.

    Args:
      depot: The depot being bisected.
      revision: Current revision we're synced to.

    Returns:
      True if we should skip building/testing this revision.
    """
    if depot == 'chromium':
      cmd = ['diff-tree', '--no-commit-id', '--name-only', '-r', revision]
      output = bisect_utils.CheckRunGit(cmd)

      files = output.splitlines()

      if len(files) == 1 and files[0] == 'DEPS':
        return True

    return False

  def RunTest(self, revision, depot, command, metric, skippable=False):
    """Performs a full sync/build/run of the specified revision.

    Args:
      revision: The revision to sync to.
      depot: The depot that's being used at the moment (src, webkit, etc.)
      command: The command to execute the performance test.
      metric: The performance metric being tested.

    Returns:
      On success, a tuple containing the results of the performance test.
      Otherwise, a tuple with the error message.
    """
    logging.info('Running RunTest with rev "%s", command "%s"',
                 revision, command)
    # Decide which sync program to use.
    sync_client = None
    if depot == 'chromium' or depot == 'android-chrome':
      sync_client = 'gclient'

    # Do the syncing for all depots.
    if not self.opts.debug_ignore_sync:
      if not self._SyncRevision(depot, revision, sync_client):
        return ('Failed to sync: [%s]' % str(revision), BUILD_RESULT_FAIL)

    # Try to do any post-sync steps. This may include "gclient runhooks".
    if not self._RunPostSync(depot):
      return ('Failed to run [gclient runhooks].', BUILD_RESULT_FAIL)

    # Skip this revision if it can be skipped.
    if skippable and self.ShouldSkipRevision(depot, revision):
      return ('Skipped revision: [%s]' % str(revision),
              BUILD_RESULT_SKIPPED)

    # Obtain a build for this revision. This may be done by requesting a build
    # from another builder, waiting for it and downloading it.
    start_build_time = time.time()
    build_success = self.ObtainBuild(depot, revision)
    if not build_success:
      return ('Failed to build revision: [%s]' % str(revision),
              BUILD_RESULT_FAIL)
    after_build_time = time.time()

    # Possibly alter the command.
    command = self.GetCompatibleCommand(command, revision, depot)

    # Run the command and get the results.
    results = self.RunPerformanceTestAndParseResults(command, metric)

    # Restore build output directory once the tests are done, to avoid
    # any discrepancies.
    if self.IsDownloadable(depot) and revision:
      self.BackupOrRestoreOutputDirectory(restore=True)

    # A value other than 0 indicates that the test couldn't be run, and results
    # should also include an error message.
    if results[1] != 0:
      return results

    external_revisions = self._Get3rdPartyRevisions(depot)

    if not external_revisions is None:
      return (results[0], results[1], external_revisions,
          time.time() - after_build_time, after_build_time -
          start_build_time)
    else:
      return ('Failed to parse DEPS file for external revisions.',
               BUILD_RESULT_FAIL)

  def _SyncRevision(self, depot, revision, sync_client):
    """Syncs depot to particular revision.

    Args:
      depot: The depot that's being used at the moment (src, webkit, etc.)
      revision: The revision to sync to.
      sync_client: Program used to sync, e.g. "gclient". Can be None.

    Returns:
      True if successful, False otherwise.
    """
    self.depot_registry.ChangeToDepotDir(depot)

    if sync_client:
      self.PerformPreBuildCleanup()

    # When using gclient to sync, you need to specify the depot you
    # want so that all the dependencies sync properly as well.
    # i.e. gclient sync src@<SHA1>
    if sync_client == 'gclient':
      revision = '%s@%s' % (bisect_utils.DEPOT_DEPS_NAME[depot]['src'],
          revision)

    return source_control.SyncToRevision(revision, sync_client)

  def _CheckIfRunPassed(self, current_value, known_good_value, known_bad_value):
    """Given known good and bad values, decide if the current_value passed
    or failed.

    Args:
      current_value: The value of the metric being checked.
      known_bad_value: The reference value for a "failed" run.
      known_good_value: The reference value for a "passed" run.

    Returns:
      True if the current_value is closer to the known_good_value than the
      known_bad_value.
    """
    if self.opts.bisect_mode == bisect_utils.BISECT_MODE_STD_DEV:
      dist_to_good_value = abs(current_value['std_dev'] -
          known_good_value['std_dev'])
      dist_to_bad_value = abs(current_value['std_dev'] -
          known_bad_value['std_dev'])
    else:
      dist_to_good_value = abs(current_value['mean'] - known_good_value['mean'])
      dist_to_bad_value = abs(current_value['mean'] - known_bad_value['mean'])

    return dist_to_good_value < dist_to_bad_value

  def _GetV8BleedingEdgeFromV8TrunkIfMappable(
      self, revision, bleeding_edge_branch):
    """Gets v8 bleeding edge revision mapped to v8 revision in trunk.

    Args:
      revision: A trunk V8 revision mapped to bleeding edge revision.
      bleeding_edge_branch: Branch used to perform lookup of bleeding edge
                            revision.
    Return:
      A mapped bleeding edge revision if found, otherwise None.
    """
    commit_position = source_control.GetCommitPosition(revision)

    if bisect_utils.IsStringInt(commit_position):
      # V8 is tricky to bisect, in that there are only a few instances when
      # we can dive into bleeding_edge and get back a meaningful result.
      # Try to detect a V8 "business as usual" case, which is when:
      #  1. trunk revision N has description "Version X.Y.Z"
      #  2. bleeding_edge revision (N-1) has description "Prepare push to
      #     trunk. Now working on X.Y.(Z+1)."
      #
      # As of 01/24/2014, V8 trunk descriptions are formatted:
      # "Version 3.X.Y (based on bleeding_edge revision rZ)"
      # So we can just try parsing that out first and fall back to the old way.
      v8_dir = self.depot_registry.GetDepotDir('v8')
      v8_bleeding_edge_dir = self.depot_registry.GetDepotDir('v8_bleeding_edge')

      revision_info = source_control.QueryRevisionInfo(revision, cwd=v8_dir)
      version_re = re.compile("Version (?P<values>[0-9,.]+)")
      regex_results = version_re.search(revision_info['subject'])
      if regex_results:
        git_revision = None
        if 'based on bleeding_edge' in revision_info['subject']:
          try:
            bleeding_edge_revision = revision_info['subject'].split(
                'bleeding_edge revision r')[1]
            bleeding_edge_revision = int(bleeding_edge_revision.split(')')[0])
            bleeding_edge_url = ('https://v8.googlecode.com/svn/branches/'
                                 'bleeding_edge@%s' % bleeding_edge_revision)
            cmd = ['log',
                   '--format=%H',
                   '--grep',
                   bleeding_edge_url,
                   '-1',
                   bleeding_edge_branch]
            output = bisect_utils.CheckRunGit(cmd, cwd=v8_dir)
            if output:
              git_revision = output.strip()
            return git_revision
          except (IndexError, ValueError):
            pass
        else:
          # V8 rolls description changed after V8 git migration, new description
          # includes "Version 3.X.Y (based on <git hash>)"
          try:
            rxp = re.compile('based on (?P<git_revision>[a-fA-F0-9]+)')
            re_results = rxp.search(revision_info['subject'])
            if re_results:
              return re_results.group('git_revision')
          except (IndexError, ValueError):
            pass
        if not git_revision:
          # Wasn't successful, try the old way of looking for "Prepare push to"
          git_revision = source_control.ResolveToRevision(
              int(commit_position) - 1, 'v8_bleeding_edge',
              bisect_utils.DEPOT_DEPS_NAME, -1, cwd=v8_bleeding_edge_dir)

          if git_revision:
            revision_info = source_control.QueryRevisionInfo(git_revision,
                cwd=v8_bleeding_edge_dir)

            if 'Prepare push to trunk' in revision_info['subject']:
              return git_revision
    return None

  def _GetNearestV8BleedingEdgeFromTrunk(
      self, revision, v8_branch, bleeding_edge_branch, search_forward=True):
    """Gets the nearest V8 roll and maps to bleeding edge revision.

    V8 is a bit tricky to bisect since it isn't just rolled out like blink.
    Each revision on trunk might just be whatever was in bleeding edge, rolled
    directly out. Or it could be some mixture of previous v8 trunk versions,
    with bits and pieces cherry picked out from bleeding edge. In order to
    bisect, we need both the before/after versions on trunk v8 to be just pushes
    from bleeding edge. With the V8 git migration, the branches got switched.
    a) master (external/v8) == candidates (v8/v8)
    b) bleeding_edge (external/v8) == master (v8/v8)

    Args:
      revision: A V8 revision to get its nearest bleeding edge revision
      search_forward: Searches forward if True, otherwise search backward.

    Return:
      A mapped bleeding edge revision if found, otherwise None.
    """
    cwd = self.depot_registry.GetDepotDir('v8')
    cmd = ['log', '--format=%ct', '-1', revision]
    output = bisect_utils.CheckRunGit(cmd, cwd=cwd)
    commit_time = int(output)
    commits = []
    if search_forward:
      cmd = ['log',
             '--format=%H',
             '--after=%d' % commit_time,
             v8_branch,
             '--reverse']
      output = bisect_utils.CheckRunGit(cmd, cwd=cwd)
      output = output.split()
      commits = output
      #Get 10 git hashes immediately after the given commit.
      commits = commits[:10]
    else:
      cmd = ['log',
             '--format=%H',
             '-10',
             '--before=%d' % commit_time,
             v8_branch]
      output = bisect_utils.CheckRunGit(cmd, cwd=cwd)
      output = output.split()
      commits = output

    bleeding_edge_revision = None

    for c in commits:
      bleeding_edge_revision = self._GetV8BleedingEdgeFromV8TrunkIfMappable(
          c, bleeding_edge_branch)
      if bleeding_edge_revision:
        break

    return bleeding_edge_revision

  def _FillInV8BleedingEdgeInfo(self, min_revision_state, max_revision_state):
    cwd = self.depot_registry.GetDepotDir('v8')
    # when "remote.origin.url" is https://chromium.googlesource.com/v8/v8.git
    v8_branch = 'origin/candidates'
    bleeding_edge_branch = 'origin/master'

    # Support for the chromium revisions with external V8 repo.
    # ie https://chromium.googlesource.com/external/v8.git
    cmd = ['config', '--get', 'remote.origin.url']
    v8_repo_url = bisect_utils.CheckRunGit(cmd, cwd=cwd)

    if 'external/v8.git' in v8_repo_url:
      v8_branch = 'origin/master'
      bleeding_edge_branch = 'origin/bleeding_edge'

    r1 = self._GetNearestV8BleedingEdgeFromTrunk(min_revision_state.revision,
        v8_branch, bleeding_edge_branch, search_forward=True)
    r2 = self._GetNearestV8BleedingEdgeFromTrunk(max_revision_state.revision,
        v8_branch, bleeding_edge_branch, search_forward=False)
    min_revision_state.external['v8_bleeding_edge'] = r1
    max_revision_state.external['v8_bleeding_edge'] = r2

    if (not self._GetV8BleedingEdgeFromV8TrunkIfMappable(
            min_revision_state.revision, bleeding_edge_branch)
        or not self._GetV8BleedingEdgeFromV8TrunkIfMappable(
            max_revision_state.revision, bleeding_edge_branch)):
      self.warnings.append(
          'Trunk revisions in V8 did not map directly to bleeding_edge. '
          'Attempted to expand the range to find V8 rolls which did map '
          'directly to bleeding_edge revisions, but results might not be '
          'valid.')

  def _FindNextDepotToBisect(
      self, current_depot, min_revision_state, max_revision_state):
    """Decides which depot the script should dive into next (if any).

    Args:
      current_depot: Current depot being bisected.
      min_revision_state: State of the earliest revision in the bisect range.
      max_revision_state: State of the latest revision in the bisect range.

    Returns:
      Name of the depot to bisect next, or None.
    """
    external_depot = None
    for next_depot in bisect_utils.DEPOT_NAMES:
      if bisect_utils.DEPOT_DEPS_NAME[next_depot].has_key('platform'):
        if bisect_utils.DEPOT_DEPS_NAME[next_depot]['platform'] != os.name:
          continue

      if not (bisect_utils.DEPOT_DEPS_NAME[next_depot]['recurse']
              and min_revision_state.depot
              in bisect_utils.DEPOT_DEPS_NAME[next_depot]['from']):
        continue

      if current_depot == 'v8':
        # We grab the bleeding_edge info here rather than earlier because we
        # finally have the revision range. From that we can search forwards and
        # backwards to try to match trunk revisions to bleeding_edge.
        self._FillInV8BleedingEdgeInfo(min_revision_state, max_revision_state)

      if (min_revision_state.external.get(next_depot) ==
          max_revision_state.external.get(next_depot)):
        continue

      if (min_revision_state.external.get(next_depot) and
          max_revision_state.external.get(next_depot)):
        external_depot = next_depot
        break

    return external_depot

  def PrepareToBisectOnDepot(
      self, current_depot, start_revision, end_revision, previous_revision):
    """Changes to the appropriate directory and gathers a list of revisions
    to bisect between |start_revision| and |end_revision|.

    Args:
      current_depot: The depot we want to bisect.
      start_revision: Start of the revision range.
      end_revision: End of the revision range.
      previous_revision: The last revision we synced to on |previous_depot|.

    Returns:
      A list containing the revisions between |start_revision| and
      |end_revision| inclusive.
    """
    # Change into working directory of external library to run
    # subsequent commands.
    self.depot_registry.ChangeToDepotDir(current_depot)

    # V8 (and possibly others) is merged in periodically. Bisecting
    # this directory directly won't give much good info.
    if bisect_utils.DEPOT_DEPS_NAME[current_depot].has_key('custom_deps'):
      config_path = os.path.join(self.src_cwd, '..')
      if bisect_utils.RunGClientAndCreateConfig(
          self.opts, bisect_utils.DEPOT_DEPS_NAME[current_depot]['custom_deps'],
          cwd=config_path):
        return []
      if bisect_utils.RunGClient(
          ['sync', '--revision', previous_revision], cwd=self.src_cwd):
        return []

    if current_depot == 'v8_bleeding_edge':
      self.depot_registry.ChangeToDepotDir('chromium')

      shutil.move('v8', 'v8.bak')
      shutil.move('v8_bleeding_edge', 'v8')

      self.cleanup_commands.append(['mv', 'v8', 'v8_bleeding_edge'])
      self.cleanup_commands.append(['mv', 'v8.bak', 'v8'])

      self.depot_registry.SetDepotDir('v8_bleeding_edge',
                                  os.path.join(self.src_cwd, 'v8'))
      self.depot_registry.SetDepotDir('v8', os.path.join(self.src_cwd,
                                                         'v8.bak'))

      self.depot_registry.ChangeToDepotDir(current_depot)

    depot_revision_list = self.GetRevisionList(current_depot,
                                               end_revision,
                                               start_revision)

    self.depot_registry.ChangeToDepotDir('chromium')

    return depot_revision_list

  def GatherReferenceValues(self, good_rev, bad_rev, cmd, metric, target_depot):
    """Gathers reference values by running the performance tests on the
    known good and bad revisions.

    Args:
      good_rev: The last known good revision where the performance regression
        has not occurred yet.
      bad_rev: A revision where the performance regression has already occurred.
      cmd: The command to execute the performance test.
      metric: The metric being tested for regression.

    Returns:
      A tuple with the results of building and running each revision.
    """
    bad_run_results = self.RunTest(bad_rev, target_depot, cmd, metric)

    good_run_results = None

    if not bad_run_results[1]:
      good_run_results = self.RunTest(good_rev, target_depot, cmd, metric)

    return (bad_run_results, good_run_results)

  def PrintRevisionsToBisectMessage(self, revision_list, depot):
    if self.opts.output_buildbot_annotations:
      step_name = 'Bisection Range: [%s:%s - %s]' % (depot, revision_list[-1],
                                                     revision_list[0])
      bisect_utils.OutputAnnotationStepStart(step_name)

    print
    print 'Revisions to bisect on [%s]:' % depot
    for revision_id in revision_list:
      print '  -> %s' % (revision_id, )
    print

    if self.opts.output_buildbot_annotations:
      bisect_utils.OutputAnnotationStepClosed()

  def NudgeRevisionsIfDEPSChange(self, bad_revision, good_revision,
                                 good_svn_revision=None):
    """Checks to see if changes to DEPS file occurred, and that the revision
    range also includes the change to .DEPS.git. If it doesn't, attempts to
    expand the revision range to include it.

    Args:
      bad_revision: First known bad git revision.
      good_revision: Last known good git revision.
      good_svn_revision: Last known good svn revision.

    Returns:
      A tuple with the new bad and good revisions.
    """
    # DONOT perform nudge because at revision 291563 .DEPS.git was removed
    # and source contain only DEPS file for dependency changes.
    if good_svn_revision >= 291563:
      return (bad_revision, good_revision)

    if self.opts.target_platform == 'chromium':
      changes_to_deps = source_control.QueryFileRevisionHistory(
          bisect_utils.FILE_DEPS, good_revision, bad_revision)

      if changes_to_deps:
        # DEPS file was changed, search from the oldest change to DEPS file to
        # bad_revision to see if there are matching .DEPS.git changes.
        oldest_deps_change = changes_to_deps[-1]
        changes_to_gitdeps = source_control.QueryFileRevisionHistory(
            bisect_utils.FILE_DEPS_GIT, oldest_deps_change, bad_revision)

        if len(changes_to_deps) != len(changes_to_gitdeps):
          # Grab the timestamp of the last DEPS change
          cmd = ['log', '--format=%ct', '-1', changes_to_deps[0]]
          output = bisect_utils.CheckRunGit(cmd)
          commit_time = int(output)

          # Try looking for a commit that touches the .DEPS.git file in the
          # next 15 minutes after the DEPS file change.
          cmd = ['log', '--format=%H', '-1',
              '--before=%d' % (commit_time + 900), '--after=%d' % commit_time,
              'origin/master', '--', bisect_utils.FILE_DEPS_GIT]
          output = bisect_utils.CheckRunGit(cmd)
          output = output.strip()
          if output:
            self.warnings.append('Detected change to DEPS and modified '
                'revision range to include change to .DEPS.git')
            return (output, good_revision)
          else:
            self.warnings.append('Detected change to DEPS but couldn\'t find '
                'matching change to .DEPS.git')
    return (bad_revision, good_revision)

  def CheckIfRevisionsInProperOrder(
      self, target_depot, good_revision, bad_revision):
    """Checks that |good_revision| is an earlier revision than |bad_revision|.

    Args:
      good_revision: Number/tag of the known good revision.
      bad_revision: Number/tag of the known bad revision.

    Returns:
      True if the revisions are in the proper order (good earlier than bad).
    """
    cwd = self.depot_registry.GetDepotDir(target_depot)
    good_position = source_control.GetCommitPosition(good_revision, cwd)
    bad_position = source_control.GetCommitPosition(bad_revision, cwd)

    return good_position <= bad_position

  def CanPerformBisect(self, good_revision, bad_revision):
    """Checks whether a given revision is bisectable.

    Checks for following:
    1. Non-bisectable revsions for android bots (refer to crbug.com/385324).
    2. Non-bisectable revsions for Windows bots (refer to crbug.com/405274).

    Args:
      good_revision: Known good revision.
      bad_revision: Known bad revision.

    Returns:
      A dictionary indicating the result. If revision is not bisectable,
      this will contain the field "error", otherwise None.
    """
    if self.opts.target_platform == 'android':
      good_revision = source_control.GetCommitPosition(good_revision)
      if (bisect_utils.IsStringInt(good_revision)
          and good_revision < 265549):
        return {'error': (
            'Bisect cannot continue for the given revision range.\n'
            'It is impossible to bisect Android regressions '
            'prior to r265549, which allows the bisect bot to '
            'rely on Telemetry to do apk installation of the most recently '
            'built local ChromeShell(refer to crbug.com/385324).\n'
            'Please try bisecting revisions greater than or equal to r265549.')}

    if bisect_utils.IsWindowsHost():
      good_revision = source_control.GetCommitPosition(good_revision)
      bad_revision = source_control.GetCommitPosition(bad_revision)
      if (bisect_utils.IsStringInt(good_revision) and
          bisect_utils.IsStringInt(bad_revision)):
        if (289987 <= good_revision < 290716 or
            289987 <= bad_revision < 290716):
          return {'error': ('Oops! Revision between r289987 and r290716 are '
                            'marked as dead zone for Windows due to '
                            'crbug.com/405274. Please try another range.')}

    return None

  def Run(self, command_to_run, bad_revision_in, good_revision_in, metric):
    """Given known good and bad revisions, run a binary search on all
    intermediate revisions to determine the CL where the performance regression
    occurred.

    Args:
      command_to_run: Specify the command to execute the performance test.
      good_revision: Number/tag of the known good revision.
      bad_revision: Number/tag of the known bad revision.
      metric: The performance metric to monitor.

    Returns:
      A BisectResults object.
    """

    # Choose depot to bisect first
    target_depot = 'chromium'
    if self.opts.target_platform == 'android-chrome':
      target_depot = 'android-chrome'

    cwd = os.getcwd()
    self.depot_registry.ChangeToDepotDir(target_depot)

    # If they passed SVN revisions, we can try match them to git SHA1 hashes.
    bad_revision = source_control.ResolveToRevision(
        bad_revision_in, target_depot, bisect_utils.DEPOT_DEPS_NAME, 100)
    good_revision = source_control.ResolveToRevision(
        good_revision_in, target_depot, bisect_utils.DEPOT_DEPS_NAME, -100)

    os.chdir(cwd)
    if bad_revision is None:
      return BisectResults(
          error='Couldn\'t resolve [%s] to SHA1.' % bad_revision_in)

    if good_revision is None:
      return BisectResults(
          error='Couldn\'t resolve [%s] to SHA1.' % good_revision_in)

    # Check that they didn't accidentally swap good and bad revisions.
    if not self.CheckIfRevisionsInProperOrder(
        target_depot, good_revision, bad_revision):
      return BisectResults(error='bad_revision < good_revision, did you swap '
                                 'these by mistake?')

    bad_revision, good_revision = self.NudgeRevisionsIfDEPSChange(
        bad_revision, good_revision, good_revision_in)
    if self.opts.output_buildbot_annotations:
      bisect_utils.OutputAnnotationStepStart('Gathering Revisions')

    cannot_bisect = self.CanPerformBisect(good_revision, bad_revision)
    if cannot_bisect:
      return BisectResults(error=cannot_bisect.get('error'))

    print 'Gathering revision range for bisection.'
    # Retrieve a list of revisions to do bisection on.
    revision_list = self.GetRevisionList(target_depot, bad_revision,
                                         good_revision)

    if self.opts.output_buildbot_annotations:
      bisect_utils.OutputAnnotationStepClosed()

    if revision_list:
      self.PrintRevisionsToBisectMessage(revision_list, target_depot)

      if self.opts.output_buildbot_annotations:
        bisect_utils.OutputAnnotationStepStart('Gathering Reference Values')

      print 'Gathering reference values for bisection.'

      # Perform the performance tests on the good and bad revisions, to get
      # reference values.
      bad_results, good_results = self.GatherReferenceValues(good_revision,
                                                             bad_revision,
                                                             command_to_run,
                                                             metric,
                                                             target_depot)

      if self.opts.output_buildbot_annotations:
        bisect_utils.OutputAnnotationStepClosed()

      if bad_results[1]:
        error = ('An error occurred while building and running the \'bad\' '
                 'reference value. The bisect cannot continue without '
                 'a working \'bad\' revision to start from.\n\nError: %s' %
                 bad_results[0])
        return BisectResults(error=error)

      if good_results[1]:
        error = ('An error occurred while building and running the \'good\' '
                 'reference value. The bisect cannot continue without '
                 'a working \'good\' revision to start from.\n\nError: %s' %
                 good_results[0])
        return BisectResults(error=error)

      # We need these reference values to determine if later runs should be
      # classified as pass or fail.
      known_bad_value = bad_results[0]
      known_good_value = good_results[0]

      # Check the direction of improvement only if the improvement_direction
      # option is set to a specific direction (1 for higher is better or -1 for
      # lower is better).
      improvement_dir = self.opts.improvement_direction
      if improvement_dir:
        higher_is_better = improvement_dir > 0
        if higher_is_better:
          message = "Expecting higher values to be better for this metric, "
        else:
          message = "Expecting lower values to be better for this metric, "
        metric_increased = known_bad_value['mean'] > known_good_value['mean']
        if metric_increased:
          message += "and the metric appears to have increased. "
        else:
          message += "and the metric appears to have decreased. "
        if ((higher_is_better and metric_increased) or
            (not higher_is_better and not metric_increased)):
          error = (message + 'Then, the test results for the ends of the given '
                   '\'good\' - \'bad\' range of revisions represent an '
                   'improvement (and not a regression).')
          return BisectResults(error=error)
        logging.info(message + "Therefore we continue to bisect.")

      bisect_state = BisectState(target_depot, revision_list)
      revision_states = bisect_state.GetRevisionStates()

      min_revision = 0
      max_revision = len(revision_states) - 1

      # Can just mark the good and bad revisions explicitly here since we
      # already know the results.
      bad_revision_state = revision_states[min_revision]
      bad_revision_state.external = bad_results[2]
      bad_revision_state.perf_time = bad_results[3]
      bad_revision_state.build_time = bad_results[4]
      bad_revision_state.passed = False
      bad_revision_state.value = known_bad_value

      good_revision_state = revision_states[max_revision]
      good_revision_state.external = good_results[2]
      good_revision_state.perf_time = good_results[3]
      good_revision_state.build_time = good_results[4]
      good_revision_state.passed = True
      good_revision_state.value = known_good_value

      # Check how likely it is that the good and bad results are different
      # beyond chance-induced variation.
      confidence_error = False
      if not self.opts.debug_ignore_regression_confidence:
        confidence_error = _CheckRegressionConfidenceError(good_revision,
                                                           bad_revision,
                                                           known_good_value,
                                                           known_bad_value)
        if confidence_error:
          self.warnings.append(confidence_error)
          bad_revision_state.passed = True # Marking the 'bad' revision as good.
          return BisectResults(bisect_state, self.depot_registry, self.opts,
                               self.warnings)

      while True:
        if not revision_states:
          break

        if max_revision - min_revision <= 1:
          min_revision_state = revision_states[min_revision]
          max_revision_state = revision_states[max_revision]
          current_depot = min_revision_state.depot
          # TODO(sergiyb): Under which conditions can first two branches be hit?
          if min_revision_state.passed == '?':
            next_revision_index = min_revision
          elif max_revision_state.passed == '?':
            next_revision_index = max_revision
          elif current_depot in ['android-chrome', 'chromium', 'v8']:
            previous_revision = revision_states[min_revision].revision
            # If there were changes to any of the external libraries we track,
            # should bisect the changes there as well.
            external_depot = self._FindNextDepotToBisect(
                current_depot, min_revision_state, max_revision_state)
            # If there was no change in any of the external depots, the search
            # is over.
            if not external_depot:
              if current_depot == 'v8':
                self.warnings.append('Unfortunately, V8 bisection couldn\'t '
                    'continue any further. The script can only bisect into '
                    'V8\'s bleeding_edge repository if both the current and '
                    'previous revisions in trunk map directly to revisions in '
                    'bleeding_edge.')
              break

            earliest_revision = max_revision_state.external[external_depot]
            latest_revision = min_revision_state.external[external_depot]

            new_revision_list = self.PrepareToBisectOnDepot(
                external_depot, earliest_revision, latest_revision,
                previous_revision)

            if not new_revision_list:
              error = ('An error occurred attempting to retrieve revision '
                       'range: [%s..%s]' % (earliest_revision, latest_revision))
              return BisectResults(error=error)

            revision_states = bisect_state.CreateRevisionStatesAfter(
                external_depot, new_revision_list, current_depot,
                previous_revision)

            # Reset the bisection and perform it on the newly inserted states.
            min_revision = 0
            max_revision = len(revision_states) - 1

            print ('Regression in metric %s appears to be the result of '
                   'changes in [%s].' % (metric, external_depot))

            revision_list = [state.revision for state in revision_states]
            self.PrintRevisionsToBisectMessage(revision_list, external_depot)

            continue
          else:
            break
        else:
          next_revision_index = (int((max_revision - min_revision) / 2) +
                                 min_revision)

        next_revision_state = revision_states[next_revision_index]
        next_revision = next_revision_state.revision
        next_depot = next_revision_state.depot

        self.depot_registry.ChangeToDepotDir(next_depot)

        message = 'Working on [%s:%s]' % (next_depot, next_revision)
        print message
        if self.opts.output_buildbot_annotations:
          bisect_utils.OutputAnnotationStepStart(message)

        run_results = self.RunTest(next_revision, next_depot, command_to_run,
                                   metric, skippable=True)

        # If the build is successful, check whether or not the metric
        # had regressed.
        if not run_results[1]:
          if len(run_results) > 2:
            next_revision_state.external = run_results[2]
            next_revision_state.perf_time = run_results[3]
            next_revision_state.build_time = run_results[4]

          passed_regression = self._CheckIfRunPassed(run_results[0],
                                                     known_good_value,
                                                     known_bad_value)

          next_revision_state.passed = passed_regression
          next_revision_state.value = run_results[0]

          if passed_regression:
            max_revision = next_revision_index
          else:
            min_revision = next_revision_index
        else:
          if run_results[1] == BUILD_RESULT_SKIPPED:
            next_revision_state.passed = 'Skipped'
          elif run_results[1] == BUILD_RESULT_FAIL:
            next_revision_state.passed = 'Build Failed'

          print run_results[0]

          # If the build is broken, remove it and redo search.
          revision_states.pop(next_revision_index)

          max_revision -= 1

        if self.opts.output_buildbot_annotations:
          self.printer.PrintPartialResults(bisect_state)
          bisect_utils.OutputAnnotationStepClosed()

      return BisectResults(bisect_state, self.depot_registry, self.opts,
                           self.warnings)
    else:
      # Weren't able to sync and retrieve the revision range.
      error = ('An error occurred attempting to retrieve revision range: '
               '[%s..%s]' % (good_revision, bad_revision))
      return BisectResults(error=error)


def _IsPlatformSupported():
  """Checks that this platform and build system are supported.

  Args:
    opts: The options parsed from the command line.

  Returns:
    True if the platform and build system are supported.
  """
  # Haven't tested the script out on any other platforms yet.
  supported = ['posix', 'nt']
  return os.name in supported


def RemoveBuildFiles(build_type):
  """Removes build files from previous runs."""
  out_dir = os.path.join('out', build_type)
  build_dir = os.path.join('build', build_type)
  logging.info('Removing build files in "%s" and "%s".',
               os.path.abspath(out_dir), os.path.abspath(build_dir))
  try:
    RemakeDirectoryTree(out_dir)
    RemakeDirectoryTree(build_dir)
  except Exception as e:
    raise RuntimeError('Got error in RemoveBuildFiles: %s' % e)


def RemakeDirectoryTree(path_to_dir):
  """Removes a directory tree and replaces it with an empty one.

  Returns True if successful, False otherwise.
  """
  RemoveDirectoryTree(path_to_dir)
  MaybeMakeDirectory(path_to_dir)


def RemoveDirectoryTree(path_to_dir):
  """Removes a directory tree. Returns True if successful or False otherwise."""
  try:
    if os.path.exists(path_to_dir):
      shutil.rmtree(path_to_dir)
  except OSError, e:
    if e.errno != errno.ENOENT:
      raise


# This is copied from build/scripts/common/chromium_utils.py.
def MaybeMakeDirectory(*path):
  """Creates an entire path, if it doesn't already exist."""
  file_path = os.path.join(*path)
  try:
    os.makedirs(file_path)
  except OSError as e:
    if e.errno != errno.EEXIST:
      raise


class BisectOptions(object):
  """Options to be used when running bisection."""
  def __init__(self):
    super(BisectOptions, self).__init__()

    self.target_platform = 'chromium'
    self.build_preference = None
    self.good_revision = None
    self.bad_revision = None
    self.use_goma = None
    self.goma_dir = None
    self.goma_threads = 64
    self.repeat_test_count = 20
    self.truncate_percent = 25
    self.max_time_minutes = 20
    self.metric = None
    self.command = None
    self.output_buildbot_annotations = None
    self.no_custom_deps = False
    self.working_directory = None
    self.extra_src = None
    self.debug_ignore_build = None
    self.debug_ignore_sync = None
    self.debug_ignore_perf_test = None
    self.debug_ignore_regression_confidence = None
    self.debug_fake_first_test_mean = 0
    self.gs_bucket = None
    self.target_arch = 'ia32'
    self.target_build_type = 'Release'
    self.builder_host = None
    self.builder_port = None
    self.bisect_mode = bisect_utils.BISECT_MODE_MEAN
    self.improvement_direction = 0
    self.bug_id = ''

  @staticmethod
  def _AddBisectOptionsGroup(parser):
    group = parser.add_argument_group('Bisect options')
    group.add_argument('-c', '--command', required=True,
                       help='A command to execute your performance test at '
                            'each point in the bisection.')
    group.add_argument('-b', '--bad_revision', required=True,
                       help='A bad revision to start bisection. Must be later '
                            'than good revision. May be either a git or svn '
                            'revision.')
    group.add_argument('-g', '--good_revision', required=True,
                       help='A revision to start bisection where performance '
                            'test is known to pass. Must be earlier than the '
                            'bad revision. May be either a git or a svn '
                            'revision.')
    group.add_argument('-m', '--metric',
                       help='The desired metric to bisect on. For example '
                            '"vm_rss_final_b/vm_rss_f_b"')
    group.add_argument('-d', '--improvement_direction', type=int, default=0,
                       help='An integer number representing the direction of '
                            'improvement. 1 for higher is better, -1 for lower '
                            'is better, 0 for ignore (default).')
    group.add_argument('-r', '--repeat_test_count', type=int, default=20,
                       choices=range(1, 101),
                       help='The number of times to repeat the performance '
                            'test. Values will be clamped to range [1, 100]. '
                            'Default value is 20.')
    group.add_argument('--max_time_minutes', type=int, default=20,
                       choices=range(1, 61),
                       help='The maximum time (in minutes) to take running the '
                            'performance tests. The script will run the '
                            'performance tests according to '
                            '--repeat_test_count, so long as it doesn\'t exceed'
                            ' --max_time_minutes. Values will be clamped to '
                            'range [1, 60]. Default value is 20.')
    group.add_argument('-t', '--truncate_percent', type=int, default=25,
                       help='The highest/lowest % are discarded to form a '
                            'truncated mean. Values will be clamped to range '
                            '[0, 25]. Default value is 25 (highest/lowest 25% '
                            'will be discarded).')
    group.add_argument('--bisect_mode', default=bisect_utils.BISECT_MODE_MEAN,
                       choices=[bisect_utils.BISECT_MODE_MEAN,
                                bisect_utils.BISECT_MODE_STD_DEV,
                                bisect_utils.BISECT_MODE_RETURN_CODE],
                       help='The bisect mode. Choices are to bisect on the '
                            'difference in mean, std_dev, or return_code.')
    group.add_argument('--bug_id', default='',
                       help='The id for the bug associated with this bisect. ' +
                            'If this number is given, bisect will attempt to ' +
                            'verify that the bug is not closed before '
                            'starting.')

  @staticmethod
  def _AddBuildOptionsGroup(parser):
    group = parser.add_argument_group('Build options')
    group.add_argument('-w', '--working_directory',
                       help='Path to the working directory where the script '
                       'will do an initial checkout of the chromium depot. The '
                       'files will be placed in a subdirectory "bisect" under '
                       'working_directory and that will be used to perform the '
                       'bisection. This parameter is optional, if it is not '
                       'supplied, the script will work from the current depot.')
    group.add_argument('--build_preference',
                       choices=['msvs', 'ninja', 'make'],
                       help='The preferred build system to use. On linux/mac '
                            'the options are make/ninja. On Windows, the '
                            'options are msvs/ninja.')
    group.add_argument('--target_platform', default='chromium',
                       choices=['chromium', 'android', 'android-chrome'],
                       help='The target platform. Choices are "chromium" '
                            '(current platform), or "android". If you specify '
                            'something other than "chromium", you must be '
                            'properly set up to build that platform.')
    group.add_argument('--no_custom_deps', dest='no_custom_deps',
                       action='store_true', default=False,
                       help='Run the script with custom_deps or not.')
    group.add_argument('--extra_src',
                       help='Path to a script which can be used to modify the '
                            'bisect script\'s behavior.')
    group.add_argument('--use_goma', action='store_true',
                       help='Add a bunch of extra threads for goma, and enable '
                            'goma')
    group.add_argument('--goma_dir',
                       help='Path to goma tools (or system default if not '
                            'specified).')
    group.add_argument('--goma_threads', type=int, default='64',
                       help='Number of threads for goma, only if using goma.')
    group.add_argument('--output_buildbot_annotations', action='store_true',
                       help='Add extra annotation output for buildbot.')
    group.add_argument('--gs_bucket', default='', dest='gs_bucket',
                       help='Name of Google Storage bucket to upload or '
                            'download build. e.g., chrome-perf')
    group.add_argument('--target_arch', default='ia32',
                       dest='target_arch', choices=['ia32', 'x64', 'arm'],
                       help='The target build architecture. Choices are "ia32" '
                            '(default), "x64" or "arm".')
    group.add_argument('--target_build_type', default='Release',
                       choices=['Release', 'Debug'],
                       help='The target build type. Choices are "Release" '
                            '(default), or "Debug".')
    group.add_argument('--builder_host', dest='builder_host',
                       help='Host address of server to produce build by '
                            'posting try job request.')
    group.add_argument('--builder_port', dest='builder_port', type=int,
                       help='HTTP port of the server to produce build by '
                            'posting try job request.')

  @staticmethod
  def _AddDebugOptionsGroup(parser):
    group = parser.add_argument_group('Debug options')
    group.add_argument('--debug_ignore_build', action='store_true',
                       help='DEBUG: Don\'t perform builds.')
    group.add_argument('--debug_ignore_sync', action='store_true',
                       help='DEBUG: Don\'t perform syncs.')
    group.add_argument('--debug_ignore_perf_test', action='store_true',
                       help='DEBUG: Don\'t perform performance tests.')
    group.add_argument('--debug_ignore_regression_confidence',
                       action='store_true',
                       help='DEBUG: Don\'t score the confidence of the initial '
                            'good and bad revisions\' test results.')
    group.add_argument('--debug_fake_first_test_mean', type=int, default='0',
                       help='DEBUG: When faking performance tests, return this '
                            'value as the mean of the first performance test, '
                            'and return a mean of 0.0 for further tests.')
    return group

  @classmethod
  def _CreateCommandLineParser(cls):
    """Creates a parser with bisect options.

    Returns:
      An instance of optparse.OptionParser.
    """
    usage = ('%prog [options] [-- chromium-options]\n'
             'Perform binary search on revision history to find a minimal '
             'range of revisions where a performance metric regressed.\n')

    parser = argparse.ArgumentParser(usage=usage)
    cls._AddBisectOptionsGroup(parser)
    cls._AddBuildOptionsGroup(parser)
    cls._AddDebugOptionsGroup(parser)
    return parser

  def ParseCommandLine(self):
    """Parses the command line for bisect options."""
    parser = self._CreateCommandLineParser()
    opts = parser.parse_args()

    try:
      if (not opts.metric and
          opts.bisect_mode != bisect_utils.BISECT_MODE_RETURN_CODE):
        raise RuntimeError('missing required parameter: --metric')

      if opts.gs_bucket:
        if not cloud_storage.List(opts.gs_bucket):
          raise RuntimeError('Invalid Google Storage: gs://%s' % opts.gs_bucket)
        if not opts.builder_host:
          raise RuntimeError('Must specify try server host name using '
                             '--builder_host when gs_bucket is used.')
        if not opts.builder_port:
          raise RuntimeError('Must specify try server port number using '
                             '--builder_port when gs_bucket is used.')

      if opts.bisect_mode != bisect_utils.BISECT_MODE_RETURN_CODE:
        metric_values = opts.metric.split('/')
        if len(metric_values) != 2:
          raise RuntimeError('Invalid metric specified: [%s]' % opts.metric)
        opts.metric = metric_values

      opts.truncate_percent = min(max(opts.truncate_percent, 0), 25) / 100.0

      for k, v in opts.__dict__.iteritems():
        assert hasattr(self, k), 'Invalid %s attribute in BisectOptions.' % k
        setattr(self, k, v)
    except RuntimeError, e:
      output_string = StringIO.StringIO()
      parser.print_help(file=output_string)
      error_message = '%s\n\n%s' % (e.message, output_string.getvalue())
      output_string.close()
      raise RuntimeError(error_message)

  @staticmethod
  def FromDict(values):
    """Creates an instance of BisectOptions from a dictionary.

    Args:
      values: a dict containing options to set.

    Returns:
      An instance of BisectOptions.
    """
    opts = BisectOptions()
    for k, v in values.iteritems():
      assert hasattr(opts, k), 'Invalid %s attribute in BisectOptions.' % k
      setattr(opts, k, v)

    if opts.metric and opts.bisect_mode != bisect_utils.BISECT_MODE_RETURN_CODE:
      metric_values = opts.metric.split('/')
      if len(metric_values) != 2:
        raise RuntimeError('Invalid metric specified: [%s]' % opts.metric)
      opts.metric = metric_values

    opts.repeat_test_count = min(max(opts.repeat_test_count, 1), 100)
    opts.max_time_minutes = min(max(opts.max_time_minutes, 1), 60)
    opts.truncate_percent = min(max(opts.truncate_percent, 0), 25)
    opts.truncate_percent = opts.truncate_percent / 100.0

    return opts


def _ConfigureLogging():
  """Trivial logging config.

  Configures logging to output any messages at or above INFO to standard out,
  without any additional formatting.
  """
  logging_format = '%(message)s'
  logging.basicConfig(
      stream=logging.sys.stdout, level=logging.INFO, format=logging_format)


def main():
  _ConfigureLogging()
  try:
    opts = BisectOptions()
    opts.ParseCommandLine()

    if opts.bug_id:
      if opts.output_buildbot_annotations:
        bisect_utils.OutputAnnotationStepStart('Checking Issue Tracker')
      issue_closed = query_crbug.CheckIssueClosed(opts.bug_id)
      if issue_closed:
        print 'Aborting bisect because bug is closed'
      else:
        print 'Could not confirm bug is closed, proceeding.'
      if opts.output_buildbot_annotations:
        bisect_utils.OutputAnnotationStepClosed()
      if issue_closed:
        results = BisectResults(abort_reason='the bug is closed.')
        bisect_test = BisectPerformanceMetrics(opts, os.getcwd())
        bisect_test.printer.FormatAndPrintResults(results)
        return 0


    if opts.extra_src:
      extra_src = bisect_utils.LoadExtraSrc(opts.extra_src)
      if not extra_src:
        raise RuntimeError('Invalid or missing --extra_src.')
      bisect_utils.AddAdditionalDepotInfo(extra_src.GetAdditionalDepotInfo())

    if opts.working_directory:
      custom_deps = bisect_utils.DEFAULT_GCLIENT_CUSTOM_DEPS
      if opts.no_custom_deps:
        custom_deps = None
      bisect_utils.CreateBisectDirectoryAndSetupDepot(opts, custom_deps)

      os.chdir(os.path.join(os.getcwd(), 'src'))
      RemoveBuildFiles(opts.target_build_type)

    if not _IsPlatformSupported():
      raise RuntimeError('Sorry, this platform isn\'t supported yet.')

    if not source_control.IsInGitRepository():
      raise RuntimeError(
          'Sorry, only the git workflow is supported at the moment.')

    # gClient sync seems to fail if you're not in master branch.
    if (not source_control.IsInProperBranch() and
        not opts.debug_ignore_sync and
        not opts.working_directory):
      raise RuntimeError('You must switch to master branch to run bisection.')
    bisect_test = BisectPerformanceMetrics(opts, os.getcwd())
    try:
      results = bisect_test.Run(opts.command, opts.bad_revision,
                                opts.good_revision, opts.metric)
      if results.error:
        raise RuntimeError(results.error)
      bisect_test.printer.FormatAndPrintResults(results)
      return 0
    finally:
      bisect_test.PerformCleanup()
  except RuntimeError as e:
    if opts.output_buildbot_annotations:
      # The perf dashboard scrapes the "results" step in order to comment on
      # bugs. If you change this, please update the perf dashboard as well.
      bisect_utils.OutputAnnotationStepStart('Results')
    print 'Runtime Error: %s' % e
    if opts.output_buildbot_annotations:
      bisect_utils.OutputAnnotationStepClosed()
  return 1


if __name__ == '__main__':
  sys.exit(main())