Add --output-dir flag for page_runner.py to specify a custom directory for
output profiling and results data.
Motivation behind this flag: I've run into a bug where a run on a local device
and a run on the try bots are showing different versions of the page. I wanted
to use the android_screen_recorder_profiler.py to record the try bot version
and see what it is actually showing. However, it currently tries to output the
video to a temporary directory in /tmp (which I do not have permission to write
to).
BUG=
Review URL: https://codereview.chromium.org/
616063004
Cr-Commit-Position: refs/heads/master@{#297740}