Add tracing AutoOpenCloseEvent.

media/blink/video_frame_compositor.h

Index: media/blink/video_frame_compositor.h
diff --git a/media/blink/video_frame_compositor.h b/media/blink/video_frame_compositor.h
index 9bb79fd056a9651221652435bc2ca29103973661..936bea867c1a7c1207c33ca286c802cc1792666b 100644
--- a/media/blink/video_frame_compositor.h
+++ b/media/blink/video_frame_compositor.h
@@ -14,6 +14,7 @@
 #include "base/synchronization/lock.h"
 #include "base/time/tick_clock.h"
 #include "base/timer/timer.h"
+#include "base/trace_event/video_playback_pae.h"
 #include "cc/layers/video_frame_provider.h"
 #include "media/base/video_renderer_sink.h"
 #include "media/blink/media_blink_export.h"
@@ -160,6 +161,9 @@ class MEDIA_BLINK_EXPORT VideoFrameCompositor
   base::Lock callback_lock_;
   VideoRendererSink::RenderCallback* callback_;
 
+  std::unique_ptr<base::trace_event::VideoPlaybackPersistentAsyncEvent>
+      persistent_async_;

[charliea (OOO until 10-5), 2016/09/08 18:26:34]

I think video_event_ might be a better name for this. persistent_async_  has to
do with tracing implementation details, whereas video_event_ is what this thing
actually is.

+
   DISALLOW_COPY_AND_ASSIGN(VideoFrameCompositor);
 };