Adds AudioDevice factory for all audio clients in Chrome

content/renderer/media/audio_message_filter.h

Index: content/renderer/media/audio_message_filter.h
diff --git a/content/renderer/media/audio_message_filter.h b/content/renderer/media/audio_message_filter.h
index 40faeabec271c8d6fbd2c8c0ec3d5c4e221d9340..85d12fd5fb72edc5b80269fe441915f083f1b5dd 100644
--- a/content/renderer/media/audio_message_filter.h
+++ b/content/renderer/media/audio_message_filter.h
@@ -39,6 +39,9 @@ class CONTENT_EXPORT AudioMessageFilter
 
   AudioMessageFilter();
 
+  // Getter for the one AudioMessageFilter object.
+  static AudioMessageFilter* current();
+
   // Add a delegate to the map and return id of the entry.
   int32 AddDelegate(Delegate* delegate);
 
@@ -75,6 +78,10 @@ class CONTENT_EXPORT AudioMessageFilter
   // changed.
   void OnStreamStateChanged(int stream_id, AudioStreamState state);
 
+  // The singleton instance for this filter.
+  // Should only be accessed on the main renderer thread.
+  static AudioMessageFilter* filter_;
+
   // A map of stream ids to delegates.
   IDMap<Delegate> delegates_;