Add support for unmixed audio from remote WebRTC remote tracks.

content/renderer/media/remote_media_stream_impl.cc

Index: content/renderer/media/remote_media_stream_impl.cc
diff --git a/content/renderer/media/remote_media_stream_impl.cc b/content/renderer/media/remote_media_stream_impl.cc
index ad8dc2145d22ca68237bcf86da7434f0d6aeb9c1..d2be9ba1e979cf4f683f52076811793bfbf068e0 100644
--- a/content/renderer/media/remote_media_stream_impl.cc
+++ b/content/renderer/media/remote_media_stream_impl.cc
@@ -231,6 +231,8 @@ void RemoteAudioTrackAdapter::InitializeWebkitAudioTrack() {
       new MediaStreamRemoteAudioTrack(observed_track().get()));
   InitializeWebkitTrack(blink::WebMediaStreamSource::TypeAudio);
   webkit_track()->setExtraData(media_stream_track.release());
+  // TODO(tommi): Set the remote audio source extra data.
+  // webkit_track()->source().setExtraData(...);
 }
 
 void RemoteAudioTrackAdapter::OnChanged() {