Add support for backgrounding processes on the Mac

content/browser/renderer_host/render_process_host_impl.cc

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Copyright 2012 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.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 
 #include <algorithm>
 #include <limits>
@@ skipping 2186 matching lines @@
   // (and hence hasn't been created yet), we will set the process priority
   // later when we create the process.
   backgrounded_ = backgrounded;
   if (!child_process_launcher_.get() || child_process_launcher_->IsStarting())
     return;
 
   // Don't background processes which have active audio streams.
   if (backgrounded_ && audio_renderer_host_->HasActiveAudio())
     return;
 
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kDisableRendererBackgrounding)) {
+    return;
+  }

[gab, 2015/06/01 19:34:20]

nit: Avoid {} (I know you like putting it all the time, but in this case it's
actually inconsistent with surrounding code which is the main Chromium style
guide rule)

[shrike, 2015/06/02 18:06:31]

It feels wrong, but you are right. Fixed.

+
 #if defined(OS_WIN)
   // The cbstext.dll loads as a global GetMessage hook in the browser process
   // and intercepts/unintercepts the kernel32 API SetPriorityClass in a
   // background thread. If the UI thread invokes this API just when it is
   // intercepted the stack is messed up on return from the interceptor
   // which causes random crashes in the browser process. Our hack for now
   // is to not invoke the SetPriorityClass API if the dll is loaded.
   if (GetModuleHandle(L"cbstext.dll"))
     return;
 #endif  // OS_WIN
 
-#if defined(OS_WIN)
-  // Same as below, but bound to an experiment (http://crbug.com/458594)
-  // initially on Windows. Enabled by default in the asbence of field trials to
-  // get coverage on the perf waterfall.
+#if defined(OS_WIN) || defined(OS_MACOSX)
+  // Same as below, but bound to an experiment (http://crbug.com/458594 on
+  // Windows, http://crbug.com/398103 on the Mac). Enabled by default in the
+  // absence of field trials to get coverage on the perf waterfall.
   base::FieldTrial* trial =
       base::FieldTrialList::Find("BackgroundRendererProcesses");
-  if (!trial || trial->group_name() != "Disallow")
+  if (!trial || !StartsWithASCII(trial->group_name(), "Disallow", true)) {
     child_process_launcher_->SetProcessBackgrounded(backgrounded);
+  }
 #else
   // Control the background state from the browser process, otherwise the task
   // telling the renderer to "unbackground" itself may be preempted by other
   // tasks executing at lowered priority ahead of it or simply by not being
   // swiftly scheduled by the OS per the low process priority
   // (http://crbug.com/398103).
   child_process_launcher_->SetProcessBackgrounded(backgrounded);
 #endif  // OS_WIN
 
   // Notify the child process of background state.
@@ skipping 221 matching lines @@
   if (worker_ref_count_ == 0)
     Cleanup();
 }
 
 void RenderProcessHostImpl::GetAudioOutputControllers(
     const GetAudioOutputControllersCallback& callback) const {
   audio_renderer_host()->GetOutputControllers(callback);
 }
 
 }  // namespace content