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 f59222e82cc563a1671f46ebe64c28d6e0aa6cb4..504c19e5a3044a637b188d2dc6a1853f1b82c7d1 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.
 
@@ -2221,14 +2221,15 @@ 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", false)) {

[gab, 2015/05/11 17:20:12]

Use case-sensitive? i.e. s/false/true?

Case-sensitive string comparison is cheaper than non-case-sensitive and I don't
see why we would need the flexibility of the latter.

[shrike, 2015/05/12 23:44:19]

Fixed. I wasn't actually sure what the right answer was here. I guess I was
thinking that a case typo would enable the experiment, which is not what we
want.

     child_process_launcher_->SetProcessBackgrounded(backgrounded);
+  }

[gab, 2015/05/11 17:20:12]

Why add the {}? It's still a single line conditional, single line body.

[shrike, 2015/05/12 23:44:19]

Yes, that is true (the style guide says either is OK). I was editing that if
statement and I always include braces on if statements (I just think it's a
safer way to code).

 #else
   // Control the background state from the browser process, otherwise the task
   // telling the renderer to "unbackground" itself may be preempted by other