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 5a7be486f07814d5cb67fbfb65a039502363dc96..d5e98e6b8ecc18c81fe4a544fb743259fb82028f 100644
--- a/content/browser/child_process_launcher.cc
+++ b/content/browser/child_process_launcher.cc
@@ -12,6 +12,7 @@
 #include "base/files/scoped_file.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/synchronization/lock.h"
@@ -503,7 +504,19 @@ void ChildProcessLauncher::Context::Terminate() {
 void ChildProcessLauncher::Context::SetProcessBackgroundedInternal(
     base::Process process,
     bool background) {
+#if defined(OS_MACOSX)
+  const std::string trial_group_name =
+      base::FieldTrialList::FindFullName("BackgroundMacRendererProcesses");
+  // Activate backgrounding when the user is part of the field trial, or
+  // there's no trial (i.e. a perf bot)
+  if (trial_group_name != "Off") {
+    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