Enable audio/video tag in content_shell

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 160 matching lines @@
 
   // A helper method to look up a AudioEntry identified by |stream_id|.
   // 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);
 
-  // Return resource_context_->media_observer() or a cached copy thereof.
-  // This is necessary because resource_context_ can be destructed before all
-  // AudioEntries have been deleted. The MediaObserver's lifetime is tied to
-  // that of the IO thread, so this is safe.
+  // Returns the MediaObserver from |resource_context_| or NULL if none exists.
   content::MediaObserver* GetMediaObserver();
 
   // A map of stream IDs to audio sources.
   AudioEntryMap audio_entries_;
 
   content::ResourceContext* resource_context_;
   AudioManager* audio_manager_;
-  content::MediaObserver* media_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererHost);
 };
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_RENDERER_HOST_H_