Add MediaCodecAudioDecoder implementation

media/base/audio_decoder.h

Index: media/base/audio_decoder.h
diff --git a/media/base/audio_decoder.h b/media/base/audio_decoder.h
index 0a3e1d3fc1ed3293a9b6ea8e112ad19e79a7f6e6..592747c3997b2c0e2e7c578be24a0153cf9770e2 100644
--- a/media/base/audio_decoder.h
+++ b/media/base/audio_decoder.h
@@ -40,9 +40,8 @@ class MEDIA_EXPORT AudioDecoder {
   // available. Only non-EOS frames should be returned via this callback.
   typedef base::Callback<void(const scoped_refptr<AudioBuffer>&)> OutputCB;
 
-  // Callback for Decode(). Called after the decoder has completed decoding
-  // corresponding DecoderBuffer, indicating that it's ready to accept another
-  // buffer to decode.
+  // Callback for Decode(). Called after the decoder has accepted corresponding
+  // DecoderBuffer, indicating that the pipeline can send next buffer to decode.
   typedef base::Callback<void(Status)> DecodeCB;
 
   AudioDecoder();