Add support for unmixed audio from remote WebRTC remote tracks.

content/renderer/media/webrtc/media_stream_remote_audio_track.h

Index: content/renderer/media/webrtc/media_stream_remote_audio_track.h
diff --git a/content/renderer/media/webrtc/media_stream_remote_audio_track.h b/content/renderer/media/webrtc/media_stream_remote_audio_track.h
index 639c2e9616bf96c3e14f3b007a37c615f5cbbab3..c54d96675d93eff0ca33d604137f50607a86924d 100644
--- a/content/renderer/media/webrtc/media_stream_remote_audio_track.h
+++ b/content/renderer/media/webrtc/media_stream_remote_audio_track.h
@@ -12,7 +12,7 @@ namespace content {
 
 // MediaStreamRemoteAudioTrack is a WebRTC specific implementation of an
 // audio track received from a PeerConnection.
-class MediaStreamRemoteAudioTrack : public MediaStreamTrack {
+class MediaStreamRemoteAudioTrack : public MediaStreamAudioTrack {

[perkj_chrome, 2015/12/11 12:31:38]

Do you in the end want to distinguish between local and remote tracks in chrome
content or do as video- have one track implementation and multiple source
implementations? 

Depending on the answer- add a todo to explain the future plan. 

[tommi (sloooow) - chröme, 2015/12/11 15:36:51]

In the end I'd like to have only one.  The video implementation makes sense to
me so I think I'll go for something similar.
This change, does make the local and remote audio tracks more similar and the
"local" source provider now works for both types.

Added a TODO.

  public:
   explicit MediaStreamRemoteAudioTrack(
       const scoped_refptr<webrtc::AudioTrackInterface>& track);
@@ -21,9 +21,15 @@ class MediaStreamRemoteAudioTrack : public MediaStreamTrack {
   void SetEnabled(bool enabled) override;
   void Stop() override;
 
+  void AddSink(MediaStreamAudioSink* sink) override;
+  void RemoveSink(MediaStreamAudioSink* sink) override;
+  media::AudioParameters GetOutputFormat() const override;
+
   webrtc::AudioTrackInterface* GetAudioAdapter() override;
 
  private:
+  class AudioSink;
+  scoped_ptr<AudioSink> sink_;
   const scoped_refptr<webrtc::AudioTrackInterface> track_;
 };