Paint first frame faster, don't crash with no frames during EOS.

media/base/null_video_sink.cc

Index: media/base/null_video_sink.cc
diff --git a/media/base/null_video_sink.cc b/media/base/null_video_sink.cc
index e96fdda240dcbc4beaa19a2286b6d6d63ce9413b..f390986394549d7ad06749257995ce1e377bff58 100644
--- a/media/base/null_video_sink.cc
+++ b/media/base/null_video_sink.cc
@@ -89,6 +89,9 @@ void NullVideoSink::CallRender() {
 }
 
 void NullVideoSink::PaintSingleFrame(const scoped_refptr<VideoFrame>& frame) {
+  if (frame == last_frame_)
+    return;
+  last_frame_ = frame;
   new_frame_cb_.Run(frame);
 }