Add tracing AutoOpenCloseEvent.

base/trace_event/persistent_async_event.h

+// 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.
+
+#ifndef BASE_TRACE_EVENT_PERSISTENT_ASYNC_H_
+#define BASE_TRACE_EVENT_PERSISTENT_ASYNC_H_
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "base/trace_event/trace_event.h"
+
+namespace base {
+
+namespace trace_event {
+
+// Note: The categories and event names must have application lifetime
+// (i.e. literals), as documented in trace_event_common.h.
+// Thus, we must make subclasses that have hard-coded categories
+// and event names, rather than passing these into the PersistentAsyncEvent.
+
+class BASE_EXPORT PersistentAsyncEvent
+    : public trace_event::TraceLog::EnabledStateObserver {
+ public:
+  PersistentAsyncEvent();
+  ~PersistentAsyncEvent() override;
+
+  void Start();

[benjhayden, 2016/08/31 03:12:53]

Can you change Start to Begin and Stop to End to be consistent with the trace
macros, both these public methods and the protected virtual methods?

[charliea (OOO until 10-5), 2016/08/31 17:30:38]

+1

[alexandermont, 2016/08/31 18:31:59]

Done

+  void Stop();
+
+  void OnTraceLogEnabled() override;
+  void OnTraceLogDisabled() override;
+
+ protected:
+  virtual void RecordStartEvent() = 0;
+  virtual void RecordStartEventWithTimestamp(int64_t timestamp) = 0;
+  virtual void RecordStopEvent() = 0;
+
+  void* id_;
+  bool active_;
+  int64_t start_time_;

[charliea (OOO until 10-5), 2016/08/31 17:30:38]

As you mentioned, I think this should be stored as a TimeTicks. Only convert it
to int64_t when you call the actual macro.

[alexandermont, 2016/08/31 18:31:59]

Done

+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_PERSISTENT_ASYNC_H_