Add tracing AutoOpenCloseEvent.

base/trace_event/auto_open_close_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/auto_open_close_event.h"
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "base/trace_event/trace_event.h"
+
+namespace base {
+namespace trace_event {
+
+AutoOpenCloseEvent::AutoOpenCloseEvent(AutoOpenCloseEvent::Type type,
+  const char* category, const char* event_name):
+  category_(category),
+  event_name_(event_name),
+  weak_factory_(this) {
+  base::trace_event::TraceLog::GetInstance()->AddAsyncEnabledStateObserver(
+      weak_factory_.GetWeakPtr());
+}
+
+AutoOpenCloseEvent::~AutoOpenCloseEvent() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  base::trace_event::TraceLog::GetInstance()->RemoveAsyncEnabledStateObserver(
+      this);
+}
+
+void AutoOpenCloseEvent::Begin() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  // We need to use the COPY version of the macro because the category and

[oystein (OOO til 10th of July), 2016/09/16 22:22:16]

Outdated comment.

[alexandermont, 2016/09/19 20:28:50]

Removed

+  // event names aren't string literals; they're passed in through
+  // the constructor.
+  TRACE_EVENT_ASYNC_BEGIN0(category_, event_name_,

[oystein (OOO til 10th of July), 2016/09/16 22:22:16]

Maybe use TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP0 as well here, since you're
reading the timestamp anyway?

[alexandermont, 2016/09/19 20:28:50]

Done

+      static_cast<void*>(this));
+  start_time_ = base::TimeTicks::Now();
+}
+
+void AutoOpenCloseEvent::End() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  TRACE_EVENT_ASYNC_END0(category_, event_name_, static_cast<void*>(this));
+  start_time_ = base::TimeTicks();
+}
+
+void AutoOpenCloseEvent::OnTraceLogEnabled() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (start_time_.ToInternalValue() != 0)
+    TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP0(
+        category_, event_name_, static_cast<void*>(this),
+        start_time_.ToInternalValue());
+}
+
+void AutoOpenCloseEvent::OnTraceLogDisabled() {}
+
+}  // namespace trace_event
+}  // namespace base