[Mac] Maximise timer slack for background tabs

base/message_loop/timer_slack.h

+// Copyright 2014 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.
+
+#ifndef BASE_MESSAGE_LOOP_TIMER_SLACK_H_
+#define BASE_MESSAGE_LOOP_TIMER_SLACK_H_
+
+namespace base {
+
+// Amount of timer slack to use for delayed timers.  Increasing timer slack
+// allows the OS to coalesce timers more effectively.
+enum TimerSlack {
+  // Lowest value for timer slack allowed by OS.
+  TIMER_SLACK_NONE,
+
+  // Maximal value for timer slack allowed by OS.
+  TIMER_SLACK_MAXIMUM
+};
+
+}  // namespace base
+
+#endif  // BASE_MESSAGE_LOOP_TIMER_SLACK_H_