Add support for backgrounding processes on the Mac

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 14006ce388f2c59fd6e83ec6256919e5f01b3bba..da046bec667241022458685a78a11970bc4e87cd 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -1,4 +1,4 @@
-// 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.
 
@@ -2205,6 +2205,12 @@ void RenderProcessHostImpl::SetBackgrounded(bool backgrounded) {
   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
@@ -2216,14 +2222,15 @@ void RenderProcessHostImpl::SetBackgrounded(bool backgrounded) {
     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