[Mac] Maximise timer slack for background tabs

content/child/child_thread.cc

 // Copyright (c) 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.
 
 #include "content/child/child_thread.h"
 
 #include <signal.h>
 
 #include <string>
 
 #include "base/allocator/allocator_extension.h"
 #include "base/base_switches.h"
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
+#include "base/message_loop/timer_slack.h"
 #include "base/process/kill.h"
 #include "base/process/process_handle.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_local.h"
 #include "base/tracked_objects.h"
 #include "components/tracing/child_trace_message_filter.h"
 #include "content/child/child_histogram_message_filter.h"
 #include "content/child/child_process.h"
@@ skipping 406 matching lines @@
     IPC_MESSAGE_HANDLER(ChildProcessMsg_Shutdown, OnShutdown)
 #if defined(IPC_MESSAGE_LOG_ENABLED)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetIPCLoggingEnabled,
                         OnSetIPCLoggingEnabled)
 #endif
     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProfilerStatus,
                         OnSetProfilerStatus)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildProfilerData,
                         OnGetChildProfilerData)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_DumpHandles, OnDumpHandles)
-#if defined(OS_WIN)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProcessBackgrounded,
                         OnProcessBackgrounded)
-#endif
 #if defined(USE_TCMALLOC)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetTcmallocStats, OnGetTcmallocStats)
 #endif
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
   if (handled)
     return true;
 
   if (msg.routing_id() == MSG_ROUTING_CONTROL)
@@ skipping 88 matching lines @@
   // race conditions if the process refcount is 0 but there's an IPC message
   // inflight that would addref it.
   Send(new ChildProcessHostMsg_ShutdownRequest);
 }
 
 void ChildThread::EnsureConnected() {
   VLOG(0) << "ChildThread::EnsureConnected()";
   base::KillProcess(base::GetCurrentProcessHandle(), 0, false);
 }
 
-#if defined(OS_WIN)
 void ChildThread::OnProcessBackgrounded(bool background) {
+  // Set timer slack to maximum on main thread when in background.
+  base::TimerSlack timer_slack = base::TIMER_SLACK_NONE;
+  if (background)
+    timer_slack = base::TIMER_SLACK_MAXIMUM;
+  base::MessageLoop::current()->SetTimerSlack(timer_slack);
+
+#ifdef OS_WIN
+  // Windows Vista+ has a fancy process backgrounding mode that can only be set
+  // from within the process.
   base::Process::Current().SetProcessBackgrounded(background);
+#endif  // OS_WIN
 }
-#endif
 
 }  // namespace content