Add tracing AutoOpenCloseEvent.

base/trace_event/persistent_async_event.cc

+// 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.
+
+#include "base/trace_event/persistent_async_event.h"
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "base/trace_event/trace_event.h"
+
+// test

[charliea (OOO until 10-5), 2016/08/29 17:27:27]

Huh?

[alexandermont, 2016/08/29 18:59:06]

Deleted. I don't remember why i put this comment there

+
+namespace base {

[charliea (OOO until 10-5), 2016/08/29 17:27:27]

As strange as it seems, I think there's normall a blank line after the start of
a new namespace:
https://cs.chromium.org/chromium/src/base/trace_event/trace_log.h?q=base/trac...

[alexandermont, 2016/08/29 18:59:06]

Done

+namespace trace_event {
+
+PersistentAsyncEvent::PersistentAsyncEvent(size_t id)
+  : id_(id), active_(false) {}
+
+PersistentAsyncEvent::~PersistentAsyncEvent() {}
+
+void PersistentAsyncEvent::Start() {
+  RecordStartEvent();
+  active_ = true;
+  start_time_ = base::TimeTicks::Now().ToInternalValue();

[charliea (OOO until 10-5), 2016/08/29 17:27:27]

Generally, if you ever find yourself using "ToInternalValue" of TimeTicks,
something's gone awry. I think here, we should really be storing the time as a
base::TimeTicks, not an int64_t.

[alexandermont, 2016/08/29 18:59:06]

The TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP0 macro takes an int64_t, not a
base::TimeTicks. What should we be doing here? Should we be storing it as a
base::TimeTicks in the PersistentAsyncEvent, and then calling ToInternalValue on
it right before putting it in the macro? Or is there something else we should be
doing?

+}
+
+void PersistentAsyncEvent::Stop() {
+  RecordStopEvent();
+  active_ = false;
+}
+
+void PersistentAsyncEvent::RecordStartEvent() {
+  TRACE_EVENT_ASYNC_BEGIN0("benchmark", "PersistentAsyncStart", id_);
+}
+
+void PersistentAsyncEvent::RecordStartEventWithTimestamp(int64_t timestamp) {
+  TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP0(
+      "benchmark", "PersistentAsyncStart", id_, timestamp);
+}
+
+void PersistentAsyncEvent::RecordStopEvent() {
+  TRACE_EVENT_ASYNC_END0("benchmark", "PersistentAsyncStop", id_);
+}
+
+void PersistentAsyncEvent::OnTraceLogEnabled() {
+  if (active_)
+  {
+    RecordStartEventWithTimestamp(start_time_);
+  }
+}
+
+void PersistentAsyncEvent::OnTraceLogDisabled() {
+  // TODO(alexandermont): How do we call RecordStopEvent before log disabled?
+  if (active_)
+  {
+    RecordStopEvent();
+  }
+}
+
+}
+}