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/trace_event/trace_event.h"
+#include <string>
+#include <ctime>
+
+namespace base {
+namespace trace_event {
+
+// Note: The categories and event names must have application lifetime

[charliea (OOO until 10-5), 2016/07/19 20:27:18]

Take a look at
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/timing/Pe...
to see how they use a non-constant trace event name

+// (strings or literals), as documented in trace_event_common.h.
+// Thus, we must makes 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:

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

These should only be indented by 1 space.

+        PersistentAsyncEvent();
+        ~PersistentAsyncEvent() override;
+
+        void Start(std::string param_value = "");
+        void Stop(std::string param_value = "");
+
+        virtual void RecordStartEvent();
+        virtual void RecordStartEventWithOffset(double offset);
+        virtual void RecordStopEvent();
+        void OnTraceLogEnabled() override;
+        void OnTraceLogDisabled() override;
+        
+        protected:

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

only indent by 1 space

+        std::string param_value_;
+
+        bool active_;
+        timeval start_time_;
+}; 
+
+}

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

}  // namespace trace_event

+}

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

}  // namespace base

+
+#endif // BASE_TRACE_EVENT_PERSISTENT_ASYNC_H_