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..70f9271e3c7484b75d2d82ad46687b6b0b9ac84e
--- /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/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();
+  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_;
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_PERSISTENT_ASYNC_H_