Add tracing AutoOpenCloseEvent.

media/blink/video_frame_compositor.cc

Index: media/blink/video_frame_compositor.cc
diff --git a/media/blink/video_frame_compositor.cc b/media/blink/video_frame_compositor.cc
index 544f7098701d481c2358c2493d2f59aae52d5256..38b8e2f80ae63650132059f614d3cbea38d9f850 100644
--- a/media/blink/video_frame_compositor.cc
+++ b/media/blink/video_frame_compositor.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/time/default_tick_clock.h"
+#include "base/trace_event/persistent_async_event.h"
 #include "base/trace_event/trace_event.h"
 #include "media/base/video_frame.h"
 
@@ -35,7 +36,11 @@ VideoFrameCompositor::VideoFrameCompositor(
       new_background_frame_(false),
       // Assume 60Hz before the first UpdateCurrentFrame() call.
       last_interval_(base::TimeDelta::FromSecondsD(1.0 / 60)),
-      callback_(nullptr) {
+      callback_(nullptr),
+      persistent_async_(new base::trace_event::PersistentAsyncEvent(
+          base::trace_event::PersistentAsyncEvent::Type::ASYNC,

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

Type is an enum, not a C++11 enum class.
I'm fine both ways. So either you make Type an "enum class", or if you keep an
enum the "::Type" part here should go away (i'm surprised this compiles. Does
it?)

+          "media,rail",
+          "VideoPlayback")) {
   background_rendering_timer_.SetTaskRunner(compositor_task_runner_);
 }
 
@@ -105,8 +110,7 @@ bool VideoFrameCompositor::HasCurrentFrame() {
 }
 
 void VideoFrameCompositor::Start(RenderCallback* callback) {
-  TRACE_EVENT_ASYNC_BEGIN0("media,rail", "VideoPlayback",
-                           static_cast<const void*>(this));
+  persistent_async_->Begin();
 
   // Called from the media thread, so acquire the callback under lock before
   // returning in case a Stop() call comes in before the PostTask is processed.
@@ -119,8 +123,7 @@ void VideoFrameCompositor::Start(RenderCallback* callback) {
 }
 
 void VideoFrameCompositor::Stop() {
-  TRACE_EVENT_ASYNC_END0("media,rail", "VideoPlayback",
-                         static_cast<const void*>(this));
+  persistent_async_->End();
 
   // Called from the media thread, so release the callback under lock before
   // returning to avoid a pending UpdateCurrentFrame() call occurring before