Add support for backgrounding processes on the Mac

content/browser/child_process_launcher.cc

Index: content/browser/child_process_launcher.cc
diff --git a/content/browser/child_process_launcher.cc b/content/browser/child_process_launcher.cc
index 28be72bb9c32eb853702adbdb0726379a3f9825c..aeb8fd3c9d52cc46eeaad95f2e9ce32d4f90d649 100644
--- a/content/browser/child_process_launcher.cc
+++ b/content/browser/child_process_launcher.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.
 
@@ -9,6 +9,7 @@
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/process/process.h"
 #include "base/profiler/scoped_tracker.h"
@@ -19,6 +20,7 @@
 #include "content/public/common/content_switches.h"
 #include "content/public/common/result_codes.h"
 #include "content/public/common/sandboxed_process_launcher_delegate.h"
+#include "content/shell/common/shell_switches.h"

[Avi (use Gerrit), 2015/04/16 02:46:20]

This is the wrong file; you mean content/public/common/content_switches.h ,
although we're already including that file.

This should fail DEPS checking; where are your trybots?

[shrike, 2015/04/16 17:31:32]

Hi Avi,

(not sure how I didn't fire up the trybots.)

I saw the other location for content_switches - what is the difference between
the two, and if I put command line switch in
content/public/common/content_switches.cc will my code that looks for the flag
still work (by content/shell/... I got the impression this was the way to pick
up flags from the command line/shell)?

 
 #if defined(OS_WIN)
 #include "base/files/file_path.h"
@@ -269,7 +271,20 @@ void TerminateOnLauncherThread(bool zygote, base::Process process) {
 void SetProcessBackgroundedOnLauncherThread(base::Process process,
                                             bool background) {
   DCHECK_CURRENTLY_ON(BrowserThread::PROCESS_LAUNCHER);
+#if defined(OS_MACOSX)
+  const std::string trial_group_name =
+      base::FieldTrialList::FindFullName("BackgroundMacRendererProcesses");

[gab, 2015/04/16 13:18:13]

As mentioned offline, I think we should use the same experiment entry point for
all platforms (i.e. in render_process_host_impl.cc).

I just wrote https://codereview.chromium.org/1089873002/ to get rid of the last
Windows-specific chunk in there, after that it should just make sense to have
the code be ifdef'ed to OS_WIN || OS_MAC (and even before that, it would have
worked, only been slightly ackward since one of the comparions would have been
against an impossible group name on Mac).

[shrike, 2015/04/21 20:55:48]

Done.

+  bool allow_background_renderers =
+      base::CommandLine::ForCurrentProcess()->HasSwitch(

[gab, 2015/04/16 18:42:42]

Don't need a command-line switch either, it comes for free with the field
trials:

chrome.exe --force-fieldtrials=BackgroundRendererProcesses/Allow/

[shrike, 2015/04/21 20:55:48]

Done.

+          switches::kBackgroundMacRendererProcesses);
+  if (allow_background_renderers || trial_group_name == "Allow") {
+    MachBroker* broker = MachBroker::GetInstance();
+    process.SetProcessBackgrounded(broker->TaskForPid(process.Pid()),
+                                   background);
+  }
+#else
   process.SetProcessBackgrounded(background);
+#endif  // defined(OS_MACOSX)
 #if defined(OS_ANDROID)
   SetChildProcessInForeground(process.Handle(), !background);
 #endif