Add tracing AutoOpenCloseEvent.

media/blink/video_frame_compositor.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BLINK_VIDEO_FRAME_COMPOSITOR_H_
 #define MEDIA_BLINK_VIDEO_FRAME_COMPOSITOR_H_
 
 #include <utility>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #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"
 #include "ui/gfx/geometry/size.h"
 
 namespace media {
 class VideoFrame;
 
 // VideoFrameCompositor acts as a bridge between the media and cc layers for
 // rendering video frames. I.e. a media::VideoRenderer will talk to this class
@@ skipping 126 matching lines @@
   base::TimeTicks last_background_render_;
 
   // These values are set on the compositor thread, but also read on the media
   // thread when the VFC is stopped.
   scoped_refptr<VideoFrame> current_frame_;
 
   // These values are updated and read from the media and compositor threads.
   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);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BLINK_VIDEO_FRAME_COMPOSITOR_H_