[Cast] Compute utilization metrics and add performance overlay.

media/cast/sender/h264_vt_encoder.cc

Index: media/cast/sender/h264_vt_encoder.cc
diff --git a/media/cast/sender/h264_vt_encoder.cc b/media/cast/sender/h264_vt_encoder.cc
index eb7bc603e35ddfbbea28b961a56c5d613fd2a352..53aaf658c415061752476f45c4b85243b1f2df05 100644
--- a/media/cast/sender/h264_vt_encoder.cc
+++ b/media/cast/sender/h264_vt_encoder.cc
@@ -729,7 +729,7 @@ void H264VideoToolboxEncoder::CompressionCallback(void* encoder_opaque,
   // frame. VideoToolbox calls the output callback serially, so this is safe.
   const uint32 frame_id = ++encoder->last_frame_id_;
 
-  scoped_ptr<EncodedFrame> encoded_frame(new EncodedFrame());
+  scoped_ptr<SenderEncodedFrame> encoded_frame(new SenderEncodedFrame());
   encoded_frame->frame_id = frame_id;
   encoded_frame->reference_time = request->reference_time;
   encoded_frame->rtp_timestamp = request->rtp_timestamp;
@@ -753,6 +753,9 @@ void H264VideoToolboxEncoder::CompressionCallback(void* encoder_opaque,
   if (has_frame_data)
     CopySampleBufferToAnnexBBuffer(sbuf, &encoded_frame->data, keyframe);
 
+  // TODO(miu): Compute and populate the |deadline_utilization| and
+  // |lossy_utilization| performance metrics in |encoded_frame|.
+
   encoder->cast_environment_->PostTask(
       CastEnvironment::MAIN, FROM_HERE,
       base::Bind(request->frame_encoded_callback,