Use AudioStreamMonitor to control power save blocking.

chrome/browser/media/audio_stream_monitor.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 CHROME_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 #define CHROME_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 
 #include <map>
 
 #include "base/callback_forward.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 namespace base {
 class TickClock;
 }
 
+namespace content {
+class PowerSaveBlocker;
+}
+
 // Repeatedly polls audio streams for their power levels, and "debounces" the
 // information into a simple, binary "was recently audible" result for the audio
 // indicators in the tab UI.  The debouncing logic is to: 1) Turn on immediately
 // when sound is audible; and 2) Hold on for X amount of time after sound has
 // gone silent, then turn off.  Said another way, we don't want tab indicators
 // to turn on/off repeatedly and annoy the user.  AudioStreamMonitor sends UI
 // update notifications only when needed, but may be queried at any time.
 //
 // There are zero or one instances of AudioStreamMonitor per
 // content::WebContents instance (referred to as "the tab" in comments below).
@@ skipping 69 matching lines @@
   // should be turned on.
   bool was_recently_audible_;
 
   // Calls Poll() at regular intervals while |poll_callbacks_| is non-empty.
   base::RepeatingTimer<AudioStreamMonitor> poll_timer_;
 
   // Started only when an indicator is toggled on, to turn it off again in the
   // future.
   base::OneShotTimer<AudioStreamMonitor> off_timer_;
 
+  // Prevent system sleep when audio is active.
+  scoped_ptr<content::PowerSaveBlocker> blocker_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_