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

media/renderers/video_renderer_impl.h

Index: media/renderers/video_renderer_impl.h
diff --git a/media/renderers/video_renderer_impl.h b/media/renderers/video_renderer_impl.h
index 3ca8cc57d4688b8a20c3675eb6d5d7bb68547368..bd4b36ddb7f6c84b0fbd5a63d0a2459e39c08958 100644
--- a/media/renderers/video_renderer_impl.h
+++ b/media/renderers/video_renderer_impl.h
@@ -17,6 +17,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
+#include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "media/base/decryptor.h"
 #include "media/base/demuxer_stream.h"
@@ -289,6 +290,10 @@ class MEDIA_EXPORT VideoRendererImpl
   // Indicates if we've painted the first valid frame after StartPlayingFrom().
   bool painted_first_frame_;
 
+  // The timestamp recorded from |tick_clock_| in StartPlayingFrom() so we could
+  // record the time needed to paint the first valid frame.
+  base::TimeTicks start_rendering_time_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<VideoRendererImpl> weak_factory_;