MediaStreamVideo*/VideoTrackAdapter and RTCVideoRenderer (small) cleanup

content/renderer/media/video_track_adapter.h

Index: content/renderer/media/video_track_adapter.h
diff --git a/content/renderer/media/video_track_adapter.h b/content/renderer/media/video_track_adapter.h
index a2f441c8155de5dccfc3af991af728a2c950f882..56aaa6a839711bea9032bf6f3bb5b00eb09de5c3 100644
--- a/content/renderer/media/video_track_adapter.h
+++ b/content/renderer/media/video_track_adapter.h
@@ -90,11 +90,11 @@ class VideoTrackAdapter
   // |thread_checker_| is bound to the main render thread.
   base::ThreadChecker thread_checker_;
 
-  scoped_refptr<base::MessageLoopProxy> io_message_loop_;
+  const scoped_refptr<base::MessageLoopProxy> io_message_loop_;
 
   // |renderer_task_runner_| is used to ensure that
   // VideoCaptureDeliverFrameCB is released on the main render thread.
-  scoped_refptr<base::SingleThreadTaskRunner> renderer_task_runner_;
+  const scoped_refptr<base::SingleThreadTaskRunner> renderer_task_runner_;
 
   // VideoFrameResolutionAdapter is an inner class that is created on the main
   // render thread but operates on the IO-thread. It does the resolution