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 2227 matching lines @@
   // 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
+  // initially on Windows. 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")
     child_process_launcher_->SetProcessBackgrounded(backgrounded);
+#elif defined(OS_MACOSX)
+  // Same as below, but bound to an experiment (http://crbug.com/458594) .
+  // Disabled by default (perf waterfall coverage will come through a new
+  // telemetry benchmark).
+  const std::string trial_group_name =
+      base::FieldTrialList::FindFullName("BackgroundRendererProcesses");
+  if (!trial_group_name.empty() && trial_group_name != "Disallow") {

[Alexei Svitkine (slow), 2015/04/23 20:53:28]

This pattern makes it impossible to have a Control group with the same behavior
as the Disallow group. 

Experimentation best practice suggest having a Control group. This used to be
handled by default when the advice was to be "off by default", but now that this
is reversed by the new launch process, you need to be more careful when setting
this up.

Either:
  1) Use experiment params rather than checking for the group name.
  2) Or change the check to not rely on a specific group name - for example you
can use StartsWith()

Please make these changes to both the Windows and Mac experiment branches, since
they suffer from the same problem.

+    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 215 matching lines @@
   if (worker_ref_count_ == 0)
     Cleanup();
 }
 
 void RenderProcessHostImpl::GetAudioOutputControllers(
     const GetAudioOutputControllersCallback& callback) const {
   audio_renderer_host()->GetOutputControllers(callback);
 }
 
 }  // namespace content