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

content/browser/renderer_host/media/audio_renderer_host.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.
 //
 // AudioRendererHost serves audio related requests from AudioRenderer which
 // lives inside the render process and provide access to audio hardware.
 //
 // This class is owned by BrowserRenderProcessHost, and instantiated on UI
 // thread, but all other operations and method calls happen on IO thread, so we
 // need to be extra careful about the lifetime of this object. AudioManager is a
@@ skipping 49 matching lines @@
 namespace content {
 
 class MediaObserver;
 class ResourceContext;
 
 class CONTENT_EXPORT AudioRendererHost
     : public BrowserMessageFilter,
       public media::AudioOutputController::EventHandler {
  public:
   // Called from UI thread from the owner of this object.
-  AudioRendererHost(media::AudioManager* audio_manager,
+  AudioRendererHost(int render_process_id,
+                    media::AudioManager* audio_manager,
                     MediaObserver* media_observer);
 
   // BrowserMessageFilter implementation.
   virtual void OnChannelClosing() OVERRIDE;
   virtual void OnDestruct() const OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message,
                                  bool* message_was_ok) OVERRIDE;
 
   // AudioOutputController::EventHandler implementations.
   virtual void OnCreated(media::AudioOutputController* controller) OVERRIDE;
@@ skipping 76 matching lines @@
   // Returns NULL if not found.
   AudioEntry* LookupById(int stream_id);
 
   // Search for a AudioEntry having the reference to |controller|.
   // This method is used to look up an AudioEntry after a controller
   // event is received.
   AudioEntry* LookupByController(media::AudioOutputController* controller);
 
   media::AudioOutputController* LookupControllerByIdForTesting(int stream_id);
 
+  int render_process_id_;
+
   // A map of stream IDs to audio sources.
   AudioEntryMap audio_entries_;
 
   media::AudioManager* audio_manager_;
   MediaObserver* media_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_RENDERER_HOST_H_