Add support for unmixed audio from remote WebRTC remote tracks.

content/renderer/media/media_stream_track.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/media_stream_track.h"
 
-#include "base/logging.h"
-#include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
-#include "third_party/libjingle/source/talk/app/webrtc/mediastreaminterface.h"
-
 namespace content {
 
 // static
 MediaStreamTrack* MediaStreamTrack::GetTrack(
     const blink::WebMediaStreamTrack& track) {
-  if (track.isNull())
-    return NULL;
-  return static_cast<MediaStreamTrack*>(track.extraData());
+  return track.isNull() ?
+      nullptr : static_cast<MediaStreamTrack*>(track.extraData());
 }
 
 MediaStreamTrack::MediaStreamTrack(bool is_local_track)
     : is_local_track_(is_local_track) {
 }
 
 MediaStreamTrack::~MediaStreamTrack() {
 }
 
-webrtc::AudioTrackInterface* MediaStreamTrack::GetAudioAdapter() {
-  NOTREACHED();
-  return nullptr;
-}
-
 }  // namespace content