[Media] Record time it takes to start rendering audio and video

media/blink/webmediaplayer_impl.cc

Index: media/blink/webmediaplayer_impl.cc
diff --git a/media/blink/webmediaplayer_impl.cc b/media/blink/webmediaplayer_impl.cc
index b6a56c2cd26dce38c4fc4676e610e77460f315e6..a1d7bb8ee3eb0c36c4a15111569c0cffaf36dffe 100644
--- a/media/blink/webmediaplayer_impl.cc
+++ b/media/blink/webmediaplayer_impl.cc
@@ -1354,6 +1354,11 @@ void WebMediaPlayerImpl::OnShown() {
   if (watch_time_reporter_)
     watch_time_reporter_->OnShown();
 
+  compositor_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&VideoFrameCompositor::SetForegroundTime,
+                 base::Unretained(compositor_), base::TimeTicks::Now()));
+
   if (IsBackgroundVideoTrackOptimizationEnabled() &&
       client_->hasSelectedVideoTrack()) {
     WebMediaPlayer::TrackId trackId = client_->getSelectedVideoTrackId();