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 3cf2a1cb22d85b54c9f9e6859097e5ac3693c4c7..f664a4be503ec1792fd3ad3e7dd64ef3313353c5 100644
--- a/media/blink/video_frame_compositor.cc
+++ b/media/blink/video_frame_compositor.cc
@@ -8,7 +8,14 @@
 #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 "media/base/video_frame.h"
+#include "base/trace_event/vfc_persistent_async_event.h"
+
+
+#include <sstream>
+#include <string>
 
 namespace media {
 
@@ -37,6 +44,12 @@ 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);
+  std::stringstream s;

[benjhayden, 2016/08/10 18:30:00]

Chrome has a handy StringPrintf library, but PersistentAsyncEvent should allow
passing a const void* to its constructor to use as the id, and allow the trace
macros to stringify it.

+  s << this_address;
+  video_id_ = s.str();
+  persistent_async_ = new base::trace_event::VFCPersistentAsyncEvent();
+  base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(persistent_async_);
 }
 
 VideoFrameCompositor::~VideoFrameCompositor() {
@@ -105,7 +118,7 @@ bool VideoFrameCompositor::HasCurrentFrame() {
 }
 
 void VideoFrameCompositor::Start(RenderCallback* callback) {
-  TRACE_EVENT0("media", "VideoFrameCompositor::Start");
+  persistent_async_->Start(video_id_);
 
   // 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.
@@ -118,7 +131,7 @@ void VideoFrameCompositor::Start(RenderCallback* callback) {
 }
 
 void VideoFrameCompositor::Stop() {
-  TRACE_EVENT0("media", "VideoFrameCompositor::Stop");
+  persistent_async_->Stop(video_id_);
 
   // Called from the media thread, so release the callback under lock before
   // returning to avoid a pending UpdateCurrentFrame() call occurring before