Add support for unmixed audio from remote WebRTC remote tracks.

content/renderer/media/media_stream_center.cc

Index: content/renderer/media/media_stream_center.cc
diff --git a/content/renderer/media/media_stream_center.cc b/content/renderer/media/media_stream_center.cc
index 53330cf3f9297efce4085d11b6f654931aa7ad20..fe39c9311b5adadcb711200cdcb4e6de39e13313 100644
--- a/content/renderer/media/media_stream_center.cc
+++ b/content/renderer/media/media_stream_center.cc
@@ -126,18 +126,17 @@ MediaStreamCenter::createWebAudioSourceFromMediaStreamTrack(
   DVLOG(1) << "MediaStreamCenter::createWebAudioSourceFromMediaStreamTrack";
   MediaStreamTrack* media_stream_track =
       static_cast<MediaStreamTrack*>(track.extraData());
-  // Only local audio track is supported now.
-  // TODO(xians): Support remote audio track.
-  if (!media_stream_track || !media_stream_track->is_local_track()) {
-    NOTIMPLEMENTED();
-    return NULL;
+  if (!media_stream_track) {
+    DLOG(ERROR) << "Native track missing for webaudio source.";
+    return nullptr;
   }
 
   blink::WebMediaStreamSource source = track.source();
   DCHECK_EQ(source.type(), blink::WebMediaStreamSource::TypeAudio);
-  WebRtcLocalAudioSourceProvider* source_provider =
-      new WebRtcLocalAudioSourceProvider(track);
-  return source_provider;
+
+  // TODO(tommi): Rename WebRtcLocalAudioSourceProvider to
+  // WebRtcAudioSourceProvider since it's not specific to local.
+  return new WebRtcLocalAudioSourceProvider(track);
 }
 
 void MediaStreamCenter::didStopLocalMediaStream(