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..bf4fb8b0009b417aa42227b8791cba7b8fbf268e 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/persistent_async_event.h"
 #include "cc/layers/video_frame_provider.h"
 #include "media/base/video_renderer_sink.h"
 #include "media/blink/media_blink_export.h"
@@ -160,6 +161,8 @@ class MEDIA_BLINK_EXPORT VideoFrameCompositor
   base::Lock callback_lock_;
   VideoRendererSink::RenderCallback* callback_;
 
+  std::unique_ptr<base::trace_event::PersistentAsyncEvent> persistent_async_;

[Primiano Tucci (use gerrit), 2016/09/15 10:08:30]

since this seems to be initialized only in the ctor, why don't you just make it
a field object (i.e. drop the unique_ptr)?
Not sure what the unique_ptr is buying here, other than an extra malloc and free
pair.

[alexandermont, 2016/09/15 21:05:13]

Done

+
   DISALLOW_COPY_AND_ASSIGN(VideoFrameCompositor);
 };