Add MuteableAudioOutputStream interface to export SetMute().

media/audio/audio_manager_base.h

Index: media/audio/audio_manager_base.h
diff --git a/media/audio/audio_manager_base.h b/media/audio/audio_manager_base.h
index cc1d10aba0bcf1c240679b73a228ea3ae8bb563b..8e2fc15b1e992f0d83559f7323597703069a7728 100644
--- a/media/audio/audio_manager_base.h
+++ b/media/audio/audio_manager_base.h
@@ -75,6 +75,12 @@ class MEDIA_EXPORT AudioManagerBase : public AudioManager {
       const std::string& device_id,
       const LogCallback& log_callback) = 0;
 
+  // Creates the output stream for the |AUDIO_BITSTREAM_XXX| format.
+  virtual AudioOutputStream* MakeBitstreamOutputStream(
+      const AudioParameters& params,
+      const std::string& device_id,
+      const LogCallback& log_callback);
+
   // Creates the input stream for the |AUDIO_PCM_LINEAR| format. The legacy
   // name is also from |AUDIO_PCM_LINEAR|.
   virtual AudioInputStream* MakeLinearInputStream(