Allow audio system to handle synchronized low-latency audio I/O

media/audio/audio_output_device.h

Index: media/audio/audio_output_device.h
===================================================================
--- media/audio/audio_output_device.h	(revision 156123)
+++ media/audio/audio_output_device.h	(working copy)
@@ -80,6 +80,9 @@
   // AudioRendererSink implementation.
   virtual void Initialize(const AudioParameters& params,
                           RenderCallback* callback) OVERRIDE;
+  virtual void InitializeIO(const AudioParameters& params,
+                            int input_channels,
+                            RenderCallback* callback) OVERRIDE;
   virtual void Start() OVERRIDE;
   virtual void Stop() OVERRIDE;
   virtual void Play() OVERRIDE;
@@ -112,7 +115,8 @@
   // The following methods are tasks posted on the IO thread that needs to
   // be executed on that thread. They interact with AudioMessageFilter and
   // sends IPC messages on that thread.
-  void CreateStreamOnIOThread(const AudioParameters& params);
+  void CreateStreamOnIOThread(const AudioParameters& params,
+                              int input_channels);
   void PlayOnIOThread();
   void PauseOnIOThread(bool flush);
   void ShutDownOnIOThread();
@@ -124,6 +128,10 @@
 
   AudioParameters audio_parameters_;
 
+  // The number of optional synchronized input channels having the same
+  // sample-rate and buffer-size as specified in audio_parameters_.
+  int input_channels_;
+
   RenderCallback* callback_;
 
   // A pointer to the IPC layer that takes care of sending requests over to