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..e51ab49d0f16feb1f8574257ef6eeece4eb37cd9 100644
--- a/media/blink/video_frame_compositor.cc
+++ b/media/blink/video_frame_compositor.cc
@@ -8,6 +8,9 @@
 #include "base/message_loop/message_loop.h"
 #include "base/time/default_tick_clock.h"
 #include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_impl.h"
+#include "base/trace_event/trace_log.h"
+#include "base/trace_event/vfc_persistent_async_event.h"
 #include "media/base/video_frame.h"
 
 namespace media {
@@ -37,6 +40,11 @@ VideoFrameCompositor::VideoFrameCompositor(
       last_interval_(base::TimeDelta::FromSecondsD(1.0 / 60)),
       callback_(nullptr) {
   background_rendering_timer_.SetTaskRunner(compositor_task_runner_);
+  const void* this_address = static_cast<const void*>(this);
+  persistent_async_ =
+      new base::trace_event::VFCPersistentAsyncEvent((size_t)(this_address));

[benjhayden, 2016/08/28 05:17:21]

Please use a C++ cast instead of C cast per style guide.
https://google.github.io/styleguide/cppguide.html#Casting
Or you could have the VFCPAE take const VFC*.

[alexandermont, 2016/08/29 18:59:07]

Done

+  base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(

[benjhayden, 2016/08/28 05:17:21]

Can you do this in the PersistentAsyncEvent constructor?

[alexandermont, 2016/08/29 18:59:07]

Done

+      persistent_async_);
 }
 
 VideoFrameCompositor::~VideoFrameCompositor() {
@@ -105,8 +113,7 @@ bool VideoFrameCompositor::HasCurrentFrame() {
 }
 
 void VideoFrameCompositor::Start(RenderCallback* callback) {
-  TRACE_EVENT_ASYNC_BEGIN0("media,rail", "VideoPlayback",
-                           static_cast<const void*>(this));
+  persistent_async_->Start();
 
   // 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 +126,7 @@ void VideoFrameCompositor::Start(RenderCallback* callback) {
 }
 
 void VideoFrameCompositor::Stop() {
-  TRACE_EVENT_ASYNC_END0("media,rail", "VideoPlayback",
-                         static_cast<const void*>(this));
+  persistent_async_->Stop();
 
   // Called from the media thread, so release the callback under lock before
   // returning to avoid a pending UpdateCurrentFrame() call occurring before