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 b28bb2f5fa8f59fd77c1ee7f6c1d77d70a0c627e..d5899c7e8bf4004ec060f722d5bd586c193ef782 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 PrefServiceSyncable;
 class Profile;
@@ -91,9 +92,15 @@ 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,
+      bool playing) OVERRIDE;
 
   scoped_refptr<MediaStreamCaptureIndicator> GetMediaStreamCaptureIndicator();
 
+  scoped_refptr<AudioStreamIndicator> GetAudioStreamIndicator();
+
  private:
   friend struct DefaultSingletonTraits<MediaCaptureDevicesDispatcher>;
 
@@ -123,6 +130,8 @@ 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_