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

chrome/browser/media/media_capture_devices_dispatcher.h

 // Copyright (c) 2012 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_MEDIA_CAPTURE_DEVICES_DISPATCHER_H_
 #define CHROME_BROWSER_MEDIA_MEDIA_CAPTURE_DEVICES_DISPATCHER_H_
 
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "base/observer_list.h"
 #include "content/public/browser/media_observer.h"
 #include "content/public/common/media_stream_request.h"
 
+class AudioStreamIndicator;
 class MediaStreamCaptureIndicator;
 class PrefServiceSyncable;
 class Profile;
 
 // This singleton is used to receive updates about media events from the content
 // layer.
 class MediaCaptureDevicesDispatcher : public content::MediaObserver {
  public:
   class Observer {
    public:
@@ skipping 59 matching lines @@
       const content::MediaStreamDevices& devices) OVERRIDE;
   virtual void OnAudioCaptureDevicesChanged(
       const content::MediaStreamDevices& devices) OVERRIDE;
   virtual void OnVideoCaptureDevicesChanged(
       const content::MediaStreamDevices& devices) OVERRIDE;
   virtual void OnMediaRequestStateChanged(
       int render_process_id,
       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>;
 
   MediaCaptureDevicesDispatcher();
   virtual ~MediaCaptureDevicesDispatcher();
 
   // Called by the MediaObserver() functions, executed on UI thread.
   void UpdateAudioDevicesOnUIThread(const content::MediaStreamDevices& devices);
   void UpdateVideoDevicesOnUIThread(const content::MediaStreamDevices& devices);
   void UpdateMediaRequestStateOnUIThread(
       int render_process_id,
       int render_view_id,
       const content::MediaStreamDevice& device,
       content::MediaRequestState state);
 
   // A list of cached audio capture devices.
   content::MediaStreamDevices audio_devices_;
 
   // A list of cached video capture devices.
   content::MediaStreamDevices video_devices_;
 
   // A list of observers for the device update notifications.
   ObserverList<Observer> observers_;
 
   // Flag to indicate if device enumeration has been done/doing.
   // Only accessed on UI thread.
   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_