[Cast] Refactor/clean-up VideoReceiver to match AudioReceiver as closely as possible.

media/cast/video_sender/codecs/vp8/vp8_encoder.cc

Index: media/cast/video_sender/codecs/vp8/vp8_encoder.cc
diff --git a/media/cast/video_sender/codecs/vp8/vp8_encoder.cc b/media/cast/video_sender/codecs/vp8/vp8_encoder.cc
index a822dc91f1e4f6061a14655a7e257cd749ddb233..8fb1695f3d52247ce37fbf33eeaa9cc53907718e 100644
--- a/media/cast/video_sender/codecs/vp8/vp8_encoder.cc
+++ b/media/cast/video_sender/codecs/vp8/vp8_encoder.cc
@@ -177,6 +177,9 @@ bool Vp8Encoder::Encode(const scoped_refptr<media::VideoFrame>& video_frame,
 
   // Note: The duration does not reflect the real time between frames. This is
   // done to keep the encoder happy.
+  //
+  // TODO(miu): This is a semi-hack.  We should consider using
+  // |video_frame->timestamp()| instead.
   uint32 duration = kVideoFrequency / cast_config_.max_frame_rate;
   if (vpx_codec_encode(encoder_.get(),
                        raw_image_,