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

media/audio/audio_output_controller.h

Index: media/audio/audio_output_controller.h
===================================================================
--- media/audio/audio_output_controller.h	(revision 155437)
+++ media/audio/audio_output_controller.h	(working copy)
@@ -92,9 +92,10 @@
     // prepare more data and perform synchronization.
     virtual void UpdatePendingBytes(uint32 bytes) = 0;
 
-    // Attempt to completely fill |audio_bus|, return the actual number of
+    // Attempt to completely fill |dest|, return the actual number of
     // frames that could be read.
-    virtual int Read(AudioBus* audio_bus) = 0;
+    // |source| may optionally be provided for input data.
+    virtual int Read(AudioBus* source, AudioBus* dest) = 0;
 
     // Close this synchronous reader.
     virtual void Close() = 0;
@@ -146,6 +147,9 @@
   // AudioSourceCallback methods.
   virtual int OnMoreData(AudioBus* audio_bus,
                          AudioBuffersState buffers_state) OVERRIDE;
+  virtual int OnMoreIOData(AudioBus* source,
+                           AudioBus* dest,
+                           AudioBuffersState buffers_state) OVERRIDE;
   virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
   virtual void WaitTillDataReady() OVERRIDE;