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..31857c9ee0bd543430d302c5e74e227c9ee39edc 100644
--- a/media/blink/video_frame_compositor.h
+++ b/media/blink/video_frame_compositor.h
@@ -19,6 +19,12 @@
 #include "media/blink/media_blink_export.h"
 #include "ui/gfx/geometry/size.h"
 
+namespace base {
+namespace trace_event {
+class AutoOpenCloseEvent;
+}
+}
+
 namespace media {
 class VideoFrame;
 
@@ -160,6 +166,9 @@ class MEDIA_BLINK_EXPORT VideoFrameCompositor
   base::Lock callback_lock_;
   VideoRendererSink::RenderCallback* callback_;
 
+  // AutoOpenCloseEvent for begin/end events.
+  std::unique_ptr<base::trace_event::AutoOpenCloseEvent> auto_open_close_;
+
   DISALLOW_COPY_AND_ASSIGN(VideoFrameCompositor);
 };