Add video frame refresh to MediaStream and VideoCapture stacks.

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 00e75faba188b6801f73a3f51218854afe3afb9a..4914de050dbddbf6bf108e66fbdd12114c008a38 100644
--- a/content/renderer/media/media_stream_video_track.cc
+++ b/content/renderer/media/media_stream_video_track.cc
@@ -212,6 +212,10 @@ blink::WebMediaStreamTrack MediaStreamVideoTrack::CreateVideoTrack(
 // static
 MediaStreamVideoTrack* MediaStreamVideoTrack::GetVideoTrack(
      const blink::WebMediaStreamTrack& track) {
+  if (track.isNull() ||
+      track.source().getType() != blink::WebMediaStreamSource::TypeVideo) {
+    return nullptr;
+  }
   return static_cast<MediaStreamVideoTrack*>(track.getExtraData());
 }
 
@@ -236,7 +240,12 @@ MediaStreamVideoTrack::MediaStreamVideoTrack(
 
 MediaStreamVideoTrack::~MediaStreamVideoTrack() {
   DCHECK(main_render_thread_checker_.CalledOnValidThread());
+
+  // It's critical to check that |sinks_| is empty because a
+  // MediaStreamVideoSink holds a pointer to this track until it calls
+  // RemoveSink().

[mcasas, 2016/04/05 23:12:52]

This is true and unfortunately so because the
ownership happens to go via Blink. With the 
Onion Soup project, however, these classes will 
migrate to Blink side and they'll become garbage 
collected, so again these ownership graphs will
need revisit.

[miu, 2016/04/06 00:03:18]

FYI--Your comment here makes me wonder if this change is conflicting w/ other
current efforts: https://codereview.chromium.org/1834323002/  If that change
lands in the next 2-3 weeks, am I good?  ;-)

   DCHECK(sinks_.empty());
+
   Stop();
   DVLOG(3) << "~MediaStreamVideoTrack()";
 }
@@ -247,9 +256,9 @@ void MediaStreamVideoTrack::AddSink(
   DCHECK(std::find(sinks_.begin(), sinks_.end(), sink) == sinks_.end());
   sinks_.push_back(sink);
   frame_deliverer_->AddCallback(sink, callback);
+
   // Request source to deliver a frame because a new sink is added.
-  if (source_)
-    source_->RequestRefreshFrame();
+  RequestRefreshFrame();
 }
 
 void MediaStreamVideoTrack::RemoveSink(MediaStreamVideoSink* sink) {
@@ -284,4 +293,10 @@ void MediaStreamVideoTrack::OnReadyStateChanged(
     sink->OnReadyStateChanged(state);
 }
 
+void MediaStreamVideoTrack::RequestRefreshFrame() {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  if (source_)
+    source_->RequestRefreshFrame();
+}
+
 }  // namespace content