Use AudioStreamMonitor to control power save blocking.

chrome/browser/media/audio_stream_monitor.h

Index: chrome/browser/media/audio_stream_monitor.h
diff --git a/chrome/browser/media/audio_stream_monitor.h b/chrome/browser/media/audio_stream_monitor.h
index 3282dbd8ba77edde54c6c35afb17bd4f49e5068e..d8279545a9a45194abe91ac414fba20841d4bfc1 100644
--- a/chrome/browser/media/audio_stream_monitor.h
+++ b/chrome/browser/media/audio_stream_monitor.h
@@ -18,6 +18,10 @@ 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
@@ -107,6 +111,9 @@ class AudioStreamMonitor
   // future.
   base::OneShotTimer<AudioStreamMonitor> off_timer_;
 
+  // Prevent system sleep when audio is active.
+  scoped_ptr<content::PowerSaveBlocker> blocker_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
 };