Clean up code to use VideoFrameMetadata::MergeMetadataFrom() when appropriate.

media/renderers/skcanvas_video_renderer.cc

Index: media/renderers/skcanvas_video_renderer.cc
diff --git a/media/renderers/skcanvas_video_renderer.cc b/media/renderers/skcanvas_video_renderer.cc
index 3ff3510a992dd99c35f35aec43f1c262dbc8aa34..129610ebd9517bb35cb47ceab556e9db25854e45 100644
--- a/media/renderers/skcanvas_video_renderer.cc
+++ b/media/renderers/skcanvas_video_renderer.cc
@@ -477,9 +477,7 @@ scoped_refptr<VideoFrame> DownShiftHighbitVideoFrame(
 
   // Copy all metadata.
   // (May be enough to copy color space)
-  base::DictionaryValue tmp;
-  video_frame->metadata()->MergeInternalValuesInto(&tmp);
-  ret->metadata()->MergeInternalValuesFrom(tmp);
+  ret->metadata()->MergeMetadataFrom(video_frame->metadata());
 
   for (int plane = VideoFrame::kYPlane; plane <= VideoFrame::kVPlane; ++plane) {
     int width = ret->row_bytes(plane);