Add tracing AutoOpenCloseEvent.

base/trace_event/video_playback_pae.h

+// Copyright 2016 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 BASE_TRACE_EVENT_VIDEO_PERSISTENT_ASYNC_H_
+#define BASE_TRACE_EVENT_VIDEO_PERSISTENT_ASYNC_H_
+
+#include "base/macros.h"
+#include "base/trace_event/persistent_async_event.h"
+
+namespace base {
+
+namespace trace_event {
+
+// Class that provides a persistent async event for video playback.

[charliea (OOO until 10-5), 2016/08/31 17:30:38]

I think "Class that..." class headers are generally discouraged (even if some of
them do exist). "A persistent async event for video playback." should be
sufficient (even if it is a sentence fragment)

[alexandermont, 2016/08/31 18:31:59]

Done

+
+class BASE_EXPORT VideoPlaybackPersistentAsyncEvent

[charliea (OOO until 10-5), 2016/08/31 17:30:38]

+oysteine@chromium.org, fmeawad@chromium.org

What are your thoughts on calling this "VideoPlaybackEvent" rather than the
wordy "VideoPlaybackPersistentAsyncEvent"? Then we could have the filename match
the class name better too (video_playback_event.h, not video_playback_pae.h)

[alexandermont, 2016/08/31 18:31:59]

I think that could be a good idea. Let's wait for confirmation from oystein or
fmeawad before changing the name in this CL

[charliea (OOO until 10-5), 2016/09/02 19:24:42]

(Pinged them directly about this)

[oystein (OOO til 10th of July), 2016/09/02 19:55:00]

Hrm, I don't think base/trace_event should reference or know about "video" or
"media" in any way. Can you generalize this, and pass the event name/category in
from somewhere else?

[benjhayden, 2016/09/02 20:47:30]

The base PersistentAsyncEvent is the generalization of this class.
I think it would make more sense to put this class in media/blink/ next to its
sole user instead of parameterizing the strings.
See how FrameBlameContext lives in content/renderer/.

+    : public PersistentAsyncEvent {
+ public:
+  VideoPlaybackPersistentAsyncEvent();
+  ~VideoPlaybackPersistentAsyncEvent() override;
+
+ protected:
+  void RecordStartEvent() override;
+  void RecordStartEventWithTimestamp(int64_t timestamp) override;
+  void RecordStopEvent() override;
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_VIDEO_PERSISTENT_ASYNC_H_