content/browser/child_process_launcher.cc

   1 // Copyright 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/browser/child_process_launcher.h"
   6
   7 #include "base/bind.h"
   8 #include "base/command_line.h"
   9 #include "base/files/file_util.h"
  10 #include "base/i18n/icu_util.h"
  11 #include "base/logging.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "base/metrics/histogram.h"
  14 #include "base/process/process.h"
  15 #include "base/profiler/scoped_tracker.h"
  16 #include "base/synchronization/lock.h"
  17 #include "base/threading/thread.h"
  18 #include "content/public/browser/content_browser_client.h"
  19 #include "content/public/common/content_descriptors.h"
  20 #include "content/public/common/content_switches.h"
  21 #include "content/public/common/result_codes.h"
  22 #include "content/public/common/sandboxed_process_launcher_delegate.h"
  23
  24 #if defined(OS_WIN)
  25 #include "base/files/file_path.h"
  26 #include "content/common/sandbox_win.h"
  27 #include "content/public/common/sandbox_init.h"
  28 #elif defined(OS_MACOSX)
  29 #include "content/browser/bootstrap_sandbox_mac.h"
  30 #include "content/browser/browser_io_surface_manager_mac.h"
  31 #include "content/browser/mach_broker_mac.h"
  32 #include "sandbox/mac/bootstrap_sandbox.h"
  33 #elif defined(OS_ANDROID)
  34 #include "base/android/jni_android.h"
  35 #include "content/browser/android/child_process_launcher_android.h"
  36 #elif defined(OS_POSIX)
  37 #include "base/memory/shared_memory.h"
  38 #include "base/memory/singleton.h"
  39 #include "content/browser/renderer_host/render_sandbox_host_linux.h"
  40 #include "content/browser/zygote_host/zygote_host_impl_linux.h"
  41 #include "content/common/child_process_sandbox_support_impl_linux.h"
  42 #endif
  43
  44 #if defined(OS_POSIX)
  45 #include "base/posix/global_descriptors.h"
  46 #include "content/browser/file_descriptor_info_impl.h"
  47 #include "gin/v8_initializer.h"
  48 #endif
  49
  50 namespace content {
  51
  52 namespace {
  53
  54 typedef base::Callback<void(bool,
  55 #if defined(OS_ANDROID)
  56                             base::ScopedFD,
  57 #endif
  58                             base::Process)> NotifyCallback;
  59
  60 void RecordHistogramsOnLauncherThread(base::TimeDelta launch_time) {
  61   DCHECK_CURRENTLY_ON(BrowserThread::PROCESS_LAUNCHER);
  62   // Log the launch time, separating out the first one (which will likely be
  63   // slower due to the rest of the browser initializing at the same time).
  64   static bool done_first_launch = false;
  65   if (done_first_launch) {
  66     UMA_HISTOGRAM_TIMES("MPArch.ChildProcessLaunchSubsequent", launch_time);
  67   } else {
  68     UMA_HISTOGRAM_TIMES("MPArch.ChildProcessLaunchFirst", launch_time);
  69     done_first_launch = true;
  70   }
  71 }
  72
  73 #if defined(OS_ANDROID)
  74 // TODO(sievers): Remove this by defining better what happens on what
  75 // thread in the corresponding Java code.
  76 void OnChildProcessStartedAndroid(const NotifyCallback& callback,
  77                                   BrowserThread::ID client_thread_id,
  78                                   const base::TimeTicks begin_launch_time,
  79                                   base::ScopedFD ipcfd,
  80                                   base::ProcessHandle handle) {
  81   // This can be called on the launcher thread or UI thread.
  82   base::TimeDelta launch_time = base::TimeTicks::Now() - begin_launch_time;
  83   BrowserThread::PostTask(
  84       BrowserThread::PROCESS_LAUNCHER, FROM_HERE,
  85       base::Bind(&RecordHistogramsOnLauncherThread, launch_time));
  86
  87   base::Closure callback_on_client_thread(
  88       base::Bind(callback, false, base::Passed(&ipcfd),
  89                  base::Passed(base::Process(handle))));
  90   if (BrowserThread::CurrentlyOn(client_thread_id)) {
  91     callback_on_client_thread.Run();
  92   } else {
  93     BrowserThread::PostTask(
  94         client_thread_id, FROM_HERE, callback_on_client_thread);
  95  }
  96 }
  97 #endif
  98
  99 void LaunchOnLauncherThread(const NotifyCallback& callback,
 100                             BrowserThread::ID client_thread_id,
 101                             int child_process_id,
 102                             SandboxedProcessLauncherDelegate* delegate,
 103 #if defined(OS_ANDROID)
 104                             base::ScopedFD ipcfd,
 105 #endif
 106                             base::CommandLine* cmd_line) {
 107   DCHECK_CURRENTLY_ON(BrowserThread::PROCESS_LAUNCHER);
 108   scoped_ptr<SandboxedProcessLauncherDelegate> delegate_deleter(delegate);
 109 #if defined(OS_WIN)
 110   bool use_zygote = false;
 111   bool launch_elevated = delegate->ShouldLaunchElevated();
 112 #elif defined(OS_MACOSX)
 113   bool use_zygote = false;
 114   base::EnvironmentMap env = delegate->GetEnvironment();
 115   base::ScopedFD ipcfd = delegate->TakeIpcFd();
 116 #elif defined(OS_POSIX) && !defined(OS_ANDROID)
 117   bool use_zygote = delegate->ShouldUseZygote();
 118   base::EnvironmentMap env = delegate->GetEnvironment();
 119   base::ScopedFD ipcfd = delegate->TakeIpcFd();
 120 #endif
 121   scoped_ptr<base::CommandLine> cmd_line_deleter(cmd_line);
 122   base::TimeTicks begin_launch_time = base::TimeTicks::Now();
 123
 124   base::Process process;
 125 #if defined(OS_WIN)
 126   if (launch_elevated) {
 127     base::LaunchOptions options;
 128     options.start_hidden = true;
 129     process = base::LaunchElevatedProcess(*cmd_line, options);
 130   } else {
 131     process = StartSandboxedProcess(delegate, cmd_line);
 132   }
 133 #elif defined(OS_POSIX)
 134   std::string process_type =
 135       cmd_line->GetSwitchValueASCII(switches::kProcessType);
 136   scoped_ptr<FileDescriptorInfo> files_to_register(
 137       FileDescriptorInfoImpl::Create());
 138
 139 #if defined(OS_ANDROID)
 140   files_to_register->Share(kPrimaryIPCChannel, ipcfd.get());
 141 #else
 142   files_to_register->Transfer(kPrimaryIPCChannel, ipcfd.Pass());
 143 #endif
 144 #endif
 145
 146 #if defined(OS_POSIX) && !defined(OS_MACOSX)
 147   std::map<int, base::MemoryMappedFile::Region> regions;
 148   GetContentClient()->browser()->GetAdditionalMappedFilesForChildProcess(
 149       *cmd_line, child_process_id, files_to_register.get());
 150 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
 151   base::PlatformFile natives_pf =
 152       gin::V8Initializer::GetOpenNativesFileForChildProcesses(
 153           &regions[kV8NativesDataDescriptor]);
 154   DCHECK_GE(natives_pf, 0);
 155   files_to_register->Share(kV8NativesDataDescriptor, natives_pf);
 156
 157   base::MemoryMappedFile::Region snapshot_region;
 158   base::PlatformFile snapshot_pf =
 159       gin::V8Initializer::GetOpenSnapshotFileForChildProcesses(
 160           &snapshot_region);
 161   // Failure to load the V8 snapshot is not necessarily an error. V8 can start
 162   // up (slower) without the snapshot.
 163   if (snapshot_pf != -1) {
 164     files_to_register->Share(kV8SnapshotDataDescriptor, snapshot_pf);
 165     regions.insert(std::make_pair(kV8SnapshotDataDescriptor, snapshot_region));
 166   }
 167
 168   if (process_type != switches::kZygoteProcess) {
 169     cmd_line->AppendSwitch(::switches::kV8NativesPassedByFD);
 170     if (snapshot_pf != -1) {
 171       cmd_line->AppendSwitch(::switches::kV8SnapshotPassedByFD);
 172     }
 173   }
 174 #endif  // defined(V8_USE_EXTERNAL_STARTUP_DATA)
 175 #endif  // defined(OS_POSIX) && !defined(OS_MACOSX)
 176
 177 #if defined(OS_ANDROID)
 178   files_to_register->Share(
 179       kAndroidICUDataDescriptor,
 180       base::i18n::GetIcuDataFileHandle(&regions[kAndroidICUDataDescriptor]));
 181
 182   // Android WebView runs in single process, ensure that we never get here
 183   // when running in single process mode.
 184   CHECK(!cmd_line->HasSwitch(switches::kSingleProcess));
 185
 186   StartChildProcess(
 187       cmd_line->argv(), child_process_id, files_to_register.Pass(), regions,
 188       base::Bind(&OnChildProcessStartedAndroid, callback, client_thread_id,
 189                  begin_launch_time, base::Passed(&ipcfd)));
 190
 191 #elif defined(OS_POSIX)
 192   // We need to close the client end of the IPC channel to reliably detect
 193   // child termination.
 194
 195 #if !defined(OS_MACOSX)
 196   if (use_zygote) {
 197     base::ProcessHandle handle = ZygoteHostImpl::GetInstance()->ForkRequest(
 198         cmd_line->argv(), files_to_register.Pass(), process_type);
 199     process = base::Process(handle);
 200   } else
 201   // Fall through to the normal posix case below when we're not zygoting.
 202 #endif  // !defined(OS_MACOSX)
 203   {
 204     // Convert FD mapping to FileHandleMappingVector
 205     base::FileHandleMappingVector fds_to_map =
 206         files_to_register->GetMappingWithIDAdjustment(
 207             base::GlobalDescriptors::kBaseDescriptor);
 208
 209 #if !defined(OS_MACOSX)
 210     if (process_type == switches::kRendererProcess) {
 211       const int sandbox_fd =
 212           RenderSandboxHostLinux::GetInstance()->GetRendererSocket();
 213       fds_to_map.push_back(std::make_pair(
 214           sandbox_fd,
 215           GetSandboxFD()));
 216     }
 217 #endif  // defined(OS_MACOSX)
 218
 219     // Actually launch the app.
 220     base::LaunchOptions options;
 221     options.environ = env;
 222     options.fds_to_remap = &fds_to_map;
 223
 224 #if defined(OS_MACOSX)
 225     // Hold the MachBroker lock for the duration of LaunchProcess. The child
 226     // will send its task port to the parent almost immediately after startup.
 227     // The Mach message will be delivered to the parent, but updating the
 228     // record of the launch will wait until after the placeholder PID is
 229     // inserted below. This ensures that while the child process may send its
 230     // port to the parent prior to the parent leaving LaunchProcess, the
 231     // order in which the record in MachBroker is updated is correct.
 232     MachBroker* broker = MachBroker::GetInstance();
 233     broker->GetLock().Acquire();
 234
 235     // Make sure the MachBroker is running, and inform it to expect a
 236     // check-in from the new process.
 237     broker->EnsureRunning();
 238
 239     // Make sure the IOSurfaceManager service is running.
 240     BrowserIOSurfaceManager::GetInstance()->EnsureRunning();
 241
 242     const int bootstrap_sandbox_policy = delegate->GetSandboxType();
 243     if (ShouldEnableBootstrapSandbox() &&
 244         bootstrap_sandbox_policy != SANDBOX_TYPE_INVALID) {
 245       options.replacement_bootstrap_name =
 246           GetBootstrapSandbox()->server_bootstrap_name();
 247       GetBootstrapSandbox()->PrepareToForkWithPolicy(
 248           bootstrap_sandbox_policy);
 249     }
 250 #endif  // defined(OS_MACOSX)
 251
 252     process = base::LaunchProcess(*cmd_line, options);
 253
 254 #if defined(OS_MACOSX)
 255     if (ShouldEnableBootstrapSandbox() &&
 256         bootstrap_sandbox_policy != SANDBOX_TYPE_INVALID) {
 257       GetBootstrapSandbox()->FinishedFork(process.Handle());
 258     }
 259
 260     if (process.IsValid())
 261       broker->AddPlaceholderForPid(process.Pid(), child_process_id);
 262
 263     // After updating the broker, release the lock and let the child's
 264     // messasge be processed on the broker's thread.
 265     broker->GetLock().Release();
 266 #endif  // defined(OS_MACOSX)
 267   }
 268 #endif  // else defined(OS_POSIX)
 269 #if !defined(OS_ANDROID)
 270   if (process.IsValid()) {
 271     RecordHistogramsOnLauncherThread(base::TimeTicks::Now() -
 272                                      begin_launch_time);
 273   }
 274   BrowserThread::PostTask(client_thread_id, FROM_HERE,
 275                           base::Bind(callback,
 276                                      use_zygote,
 277                                      base::Passed(&process)));
 278 #endif  // !defined(OS_ANDROID)
 279 }
 280
 281 void TerminateOnLauncherThread(bool zygote, base::Process process) {
 282   DCHECK_CURRENTLY_ON(BrowserThread::PROCESS_LAUNCHER);
 283 #if defined(OS_ANDROID)
 284   VLOG(1) << "ChromeProcess: Stopping process with handle "
 285           << process.Handle();
 286   StopChildProcess(process.Handle());
 287 #else
 288   // Client has gone away, so just kill the process.  Using exit code 0
 289   // means that UMA won't treat this as a crash.
 290   process.Terminate(RESULT_CODE_NORMAL_EXIT, false);
 291   // On POSIX, we must additionally reap the child.
 292 #if defined(OS_POSIX)
 293 #if !defined(OS_MACOSX)
 294   if (zygote) {
 295     // If the renderer was created via a zygote, we have to proxy the reaping
 296     // through the zygote process.
 297     ZygoteHostImpl::GetInstance()->EnsureProcessTerminated(process.Handle());
 298   } else
 299 #endif  // !OS_MACOSX
 300   base::EnsureProcessTerminated(process.Pass());
 301 #endif  // OS_POSIX
 302 #endif  // defined(OS_ANDROID)
 303 }
 304
 305 void SetProcessBackgroundedOnLauncherThread(base::Process process,
 306                                             bool background) {
 307   DCHECK_CURRENTLY_ON(BrowserThread::PROCESS_LAUNCHER);
 308 #if defined(OS_MACOSX)
 309   MachBroker* broker = MachBroker::GetInstance();
 310   mach_port_t task_port = broker->TaskForPid(process.Pid());
 311   if (task_port != TASK_NULL) {
 312     process.SetProcessBackgrounded(task_port, background);
 313   }
 314 #else
 315   process.SetProcessBackgrounded(background);
 316 #endif  // defined(OS_MACOSX)
 317 #if defined(OS_ANDROID)
 318   SetChildProcessInForeground(process.Handle(), !background);
 319 #endif
 320 }
 321
 322 }  // anonymous namespace
 323
 324 ChildProcessLauncher::ChildProcessLauncher(
 325     SandboxedProcessLauncherDelegate* delegate,
 326     base::CommandLine* cmd_line,
 327     int child_process_id,
 328     Client* client,
 329     bool terminate_on_shutdown)
 330     : client_(client),
 331       termination_status_(base::TERMINATION_STATUS_NORMAL_TERMINATION),
 332       exit_code_(RESULT_CODE_NORMAL_EXIT),
 333       zygote_(false),
 334       starting_(true),
 335 #if defined(ADDRESS_SANITIZER) || defined(LEAK_SANITIZER) ||  \
 336     defined(MEMORY_SANITIZER) || defined(THREAD_SANITIZER) || \
 337     defined(UNDEFINED_SANITIZER)
 338       terminate_child_on_shutdown_(false),
 339 #else
 340       terminate_child_on_shutdown_(terminate_on_shutdown),
 341 #endif
 342       weak_factory_(this) {
 343   DCHECK(CalledOnValidThread());
 344   CHECK(BrowserThread::GetCurrentThreadIdentifier(&client_thread_id_));
 345   Launch(delegate, cmd_line, child_process_id);
 346 }
 347
 348 ChildProcessLauncher::~ChildProcessLauncher() {
 349   DCHECK(CalledOnValidThread());
 350   if (process_.IsValid() && terminate_child_on_shutdown_) {
 351     // On Posix, EnsureProcessTerminated can lead to 2 seconds of sleep!  So
 352     // don't this on the UI/IO threads.
 353     BrowserThread::PostTask(BrowserThread::PROCESS_LAUNCHER, FROM_HERE,
 354                             base::Bind(&TerminateOnLauncherThread, zygote_,
 355                                        base::Passed(&process_)));
 356   }
 357 }
 358
 359 void ChildProcessLauncher::Launch(
 360     SandboxedProcessLauncherDelegate* delegate,
 361     base::CommandLine* cmd_line,
 362     int child_process_id) {
 363   DCHECK(CalledOnValidThread());
 364
 365 #if defined(OS_ANDROID)
 366   // Android only supports renderer, sandboxed utility and gpu.
 367   std::string process_type =
 368       cmd_line->GetSwitchValueASCII(switches::kProcessType);
 369   CHECK(process_type == switches::kGpuProcess ||
 370         process_type == switches::kRendererProcess ||
 371         process_type == switches::kUtilityProcess)
 372       << "Unsupported process type: " << process_type;
 373
 374   // Non-sandboxed utility or renderer process are currently not supported.
 375   DCHECK(process_type == switches::kGpuProcess ||
 376          !cmd_line->HasSwitch(switches::kNoSandbox));
 377
 378   // We need to close the client end of the IPC channel to reliably detect
 379   // child termination. We will close this fd after we create the child
 380   // process which is asynchronous on Android.
 381   base::ScopedFD ipcfd(delegate->TakeIpcFd().release());
 382 #endif
 383   NotifyCallback reply_callback(base::Bind(&ChildProcessLauncher::DidLaunch,
 384                                            weak_factory_.GetWeakPtr(),
 385                                            terminate_child_on_shutdown_));
 386   BrowserThread::PostTask(
 387       BrowserThread::PROCESS_LAUNCHER, FROM_HERE,
 388       base::Bind(&LaunchOnLauncherThread, reply_callback, client_thread_id_,
 389                  child_process_id, delegate,
 390 #if defined(OS_ANDROID)
 391                  base::Passed(&ipcfd),
 392 #endif
 393                  cmd_line));
 394 }
 395
 396 void ChildProcessLauncher::UpdateTerminationStatus(bool known_dead) {
 397   DCHECK(CalledOnValidThread());
 398 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
 399   if (zygote_) {
 400     termination_status_ = ZygoteHostImpl::GetInstance()->
 401         GetTerminationStatus(process_.Handle(), known_dead, &exit_code_);
 402   } else if (known_dead) {
 403     termination_status_ =
 404         base::GetKnownDeadTerminationStatus(process_.Handle(), &exit_code_);
 405   } else {
 406 #elif defined(OS_MACOSX)
 407   if (known_dead) {
 408     termination_status_ =
 409         base::GetKnownDeadTerminationStatus(process_.Handle(), &exit_code_);
 410   } else {
 411 #elif defined(OS_ANDROID)
 412   if (IsChildProcessOomProtected(process_.Handle())) {
 413     termination_status_ = base::TERMINATION_STATUS_OOM_PROTECTED;
 414   } else {
 415 #else
 416   {
 417 #endif
 418     termination_status_ =
 419       base::GetTerminationStatus(process_.Handle(), &exit_code_);
 420   }
 421 }
 422
 423 void ChildProcessLauncher::SetProcessBackgrounded(bool background) {
 424   DCHECK(CalledOnValidThread());
 425   base::Process to_pass = process_.Duplicate();
 426   BrowserThread::PostTask(BrowserThread::PROCESS_LAUNCHER, FROM_HERE,
 427                           base::Bind(&SetProcessBackgroundedOnLauncherThread,
 428                                      base::Passed(&to_pass), background));
 429 }
 430
 431 void ChildProcessLauncher::DidLaunch(
 432     base::WeakPtr<ChildProcessLauncher> instance,
 433     bool terminate_on_shutdown,
 434     bool zygote,
 435 #if defined(OS_ANDROID)
 436     base::ScopedFD ipcfd,
 437 #endif
 438     base::Process process) {
 439   if (!process.IsValid())
 440     LOG(ERROR) << "Failed to launch child process";
 441
 442   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/465841
 443   // is fixed.
 444   tracked_objects::ScopedTracker tracking_profile1(
 445       FROM_HERE_WITH_EXPLICIT_FUNCTION(
 446           "465841 ChildProcessLauncher::Context::Notify::Start"));
 447
 448   if (instance.get()) {
 449     instance->Notify(zygote,
 450 #if defined(OS_ANDROID)
 451                      ipcfd.Pass(),
 452 #endif
 453                      process.Pass());
 454   } else {
 455     // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/465841
 456     // is fixed.
 457     tracked_objects::ScopedTracker tracking_profile4(
 458         FROM_HERE_WITH_EXPLICIT_FUNCTION(
 459             "465841 ChildProcessLauncher::Context::Notify::ProcessTerminate"));
 460     if (process.IsValid() && terminate_on_shutdown) {
 461       // On Posix, EnsureProcessTerminated can lead to 2 seconds of sleep!  So
 462       // don't this on the UI/IO threads.
 463       BrowserThread::PostTask(BrowserThread::PROCESS_LAUNCHER, FROM_HERE,
 464                               base::Bind(&TerminateOnLauncherThread, zygote,
 465                                          base::Passed(&process)));
 466     }
 467   }
 468 }
 469
 470 void ChildProcessLauncher::Notify(
 471     bool zygote,
 472 #if defined(OS_ANDROID)
 473     base::ScopedFD ipcfd,
 474 #endif
 475     base::Process process) {
 476   DCHECK(CalledOnValidThread());
 477   starting_ = false;
 478   process_ = process.Pass();
 479
 480 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
 481   zygote_ = zygote;
 482 #endif
 483   if (process_.IsValid()) {
 484     // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/465841
 485     // is fixed.
 486     tracked_objects::ScopedTracker tracking_profile2(
 487         FROM_HERE_WITH_EXPLICIT_FUNCTION(
 488             "465841 ChildProcessLauncher::Context::Notify::ProcessLaunched"));
 489     client_->OnProcessLaunched();
 490   } else {
 491     // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/465841
 492     // is fixed.
 493     tracked_objects::ScopedTracker tracking_profile3(
 494         FROM_HERE_WITH_EXPLICIT_FUNCTION(
 495             "465841 ChildProcessLauncher::Context::Notify::ProcessFailed"));
 496     client_->OnProcessLaunchFailed();
 497   }
 498 }
 499
 500 bool ChildProcessLauncher::IsStarting() {
 501   // TODO(crbug.com/469248): This fails in some tests.
 502   // DCHECK(CalledOnValidThread());
 503   return starting_;
 504 }
 505
 506 const base::Process& ChildProcessLauncher::GetProcess() const {
 507   // TODO(crbug.com/469248): This fails in some tests.
 508   // DCHECK(CalledOnValidThread());
 509   return process_;
 510 }
 511
 512 base::TerminationStatus ChildProcessLauncher::GetChildTerminationStatus(
 513     bool known_dead,
 514     int* exit_code) {
 515   DCHECK(CalledOnValidThread());
 516   if (!process_.IsValid()) {
 517     // Process is already gone, so return the cached termination status.
 518     if (exit_code)
 519       *exit_code = exit_code_;
 520     return termination_status_;
 521   }
 522
 523   UpdateTerminationStatus(known_dead);
 524   if (exit_code)
 525     *exit_code = exit_code_;
 526
 527   // POSIX: If the process crashed, then the kernel closed the socket
 528   // for it and so the child has already died by the time we get
 529   // here. Since GetTerminationStatus called waitpid with WNOHANG,
 530   // it'll reap the process.  However, if GetTerminationStatus didn't
 531   // reap the child (because it was still running), we'll need to
 532   // Terminate via ProcessWatcher. So we can't close the handle here.
 533   if (termination_status_ != base::TERMINATION_STATUS_STILL_RUNNING)
 534     process_.Close();
 535
 536   return termination_status_;
 537 }
 538
 539 ChildProcessLauncher::Client* ChildProcessLauncher::ReplaceClientForTest(
 540     Client* client) {
 541   Client* ret = client_;
 542   client_ = client;
 543   return ret;
 544 }
 545
 546 }  // namespace content