Update MediaStreamTrack::Stop to latest draft.

content/renderer/media/media_stream_video_track.cc

Index: content/renderer/media/media_stream_video_track.cc
diff --git a/content/renderer/media/media_stream_video_track.cc b/content/renderer/media/media_stream_video_track.cc
index 80d202b08463cab68bd672af966fe3d2e3f06a62..4d3e3da6083a9723556a5211ae963b650c364800 100644
--- a/content/renderer/media/media_stream_video_track.cc
+++ b/content/renderer/media/media_stream_video_track.cc
@@ -57,10 +57,7 @@ MediaStreamVideoTrack::MediaStreamVideoTrack(
 
 MediaStreamVideoTrack::~MediaStreamVideoTrack() {
   DCHECK(sinks_.empty());
-  // TODO(perkj): source can be NULL if this is actually a remote video track.
-  // Remove as soon as we only have one implementation of video tracks.
-  if (source_)
-    source_->RemoveTrack(this);
+  StopTrack();
 }
 
 void MediaStreamVideoTrack::AddSink(MediaStreamVideoSink* sink) {
@@ -102,6 +99,14 @@ void MediaStreamVideoTrack::SetEnabled(bool enabled) {
   }
 }
 
+void MediaStreamVideoTrack::StopTrack() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (source_) {
+    source_->RemoveTrack(this);
+    source_ = NULL;
+  }
+}
+
 void MediaStreamVideoTrack::OnVideoFrame(
     const scoped_refptr<media::VideoFrame>& frame) {
   DCHECK(thread_checker_.CalledOnValidThread());