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

media/renderers/renderer_impl.h

Index: media/renderers/renderer_impl.h
diff --git a/media/renderers/renderer_impl.h b/media/renderers/renderer_impl.h
index 07ea2241cfb145ede0b0a233e3adc779bdcf1a23..47cece018f9374996da7da1d47f01cd3970e7950 100644
--- a/media/renderers/renderer_impl.h
+++ b/media/renderers/renderer_impl.h
@@ -195,6 +195,12 @@ class MEDIA_EXPORT RendererImpl : public Renderer {
   // runs out of data but the audio renderer still has enough.
   base::TimeDelta video_underflow_threshold_;
 
+  // Timestamps when the playback is initiated after play or seek that's set at
+  // StartPlayingFrom(). Used to calculate and report the preroll time from
+  // StartPlayingFrom() to HAVE_ENOUGH_DATA.
+  base::TimeTicks audio_preroll_start_time_;
+  base::TimeTicks video_preroll_start_time_;
+
   bool restarting_audio_ = false;
   bool restarting_video_ = false;