Add a method to tab_utils.h to find out whether a tab is playing audio.

chrome/browser/media/media_capture_devices_dispatcher.h

Index: chrome/browser/media/media_capture_devices_dispatcher.h
diff --git a/chrome/browser/media/media_capture_devices_dispatcher.h b/chrome/browser/media/media_capture_devices_dispatcher.h
index 8c3533199817ae0bd4c2c075e30d759d551176ad..bd6a0130d9969a35a59d31701e6f9c4b66602143 100644
--- a/chrome/browser/media/media_capture_devices_dispatcher.h
+++ b/chrome/browser/media/media_capture_devices_dispatcher.h
@@ -12,6 +12,7 @@
 #include "content/public/browser/media_observer.h"
 #include "content/public/common/media_stream_request.h"
 
+class AudioStreamIndicator;
 class MediaStreamCaptureIndicator;
 class PrefRegistrySyncable;
 class PrefService;
@@ -93,9 +94,16 @@ class MediaCaptureDevicesDispatcher : public content::MediaObserver {
       int render_view_id,
       const content::MediaStreamDevice& device,
       content::MediaRequestState state) OVERRIDE;
+  virtual void OnAudioStreamPlayingChanged(
+      int render_process_id,
+      int render_view_id,
+      int stream_id,
+      bool playing) OVERRIDE;
 
   scoped_refptr<MediaStreamCaptureIndicator> GetMediaStreamCaptureIndicator();
 
+  scoped_refptr<AudioStreamIndicator> GetAudioStreamIndicator();
+
  private:
   friend struct DefaultSingletonTraits<MediaCaptureDevicesDispatcher>;
 
@@ -125,6 +133,8 @@ class MediaCaptureDevicesDispatcher : public content::MediaObserver {
   bool devices_enumerated_;
 
   scoped_refptr<MediaStreamCaptureIndicator> media_stream_capture_indicator_;
+
+  scoped_refptr<AudioStreamIndicator> audio_stream_indicator_;
 };
 
 #endif  // CHROME_BROWSER_MEDIA_MEDIA_CAPTURE_DEVICES_DISPATCHER_H_