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..b85a5b87be07cf95aa1a2cacd6cede147e85e07e 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());
 }