MediaStream: Adding VideoTrackRecorder class and unittests

content/public/renderer/media_stream_video_sink.cc

 // Copyright 2013 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/public/renderer/media_stream_video_sink.h"
 
 #include "base/logging.h"
 #include "content/renderer/media/media_stream_video_track.h"
 #include "third_party/WebKit/public/platform/WebMediaStreamTrack.h"
 
 namespace content {
 
 void MediaStreamVideoSink::AddToVideoTrack(
     MediaStreamVideoSink* sink,
     const VideoCaptureDeliverFrameCB& callback,
     const blink::WebMediaStreamTrack& track) {
   DCHECK_EQ(blink::WebMediaStreamSource::TypeVideo, track.source().type());
-  MediaStreamVideoTrack* video_track =
+  MediaStreamVideoTrack* const video_track =
       static_cast<MediaStreamVideoTrack*>(track.extraData());
   video_track->AddSink(sink, callback);
 }
 
 void MediaStreamVideoSink::RemoveFromVideoTrack(
     MediaStreamVideoSink* sink,
     const blink::WebMediaStreamTrack& track) {
   DCHECK_EQ(blink::WebMediaStreamSource::TypeVideo, track.source().type());
-  MediaStreamVideoTrack* video_track =
+  MediaStreamVideoTrack* const video_track =
       static_cast<MediaStreamVideoTrack*>(track.extraData());
   video_track->RemoveSink(sink);
 }
 
 }  // namespace content