Add tracing AutoOpenCloseEvent.

base/trace_event/persistent_async_event.h

Index: base/trace_event/persistent_async_event.h
diff --git a/base/trace_event/persistent_async_event.h b/base/trace_event/persistent_async_event.h
new file mode 100644
index 0000000000000000000000000000000000000000..c31555fc88b0936aeb3240b8602e77f06d55c56d
--- /dev/null
+++ b/base/trace_event/persistent_async_event.h
@@ -0,0 +1,46 @@
+// 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_