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diff --git a/base/debug/trace_event.h b/base/debug/trace_event.h
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+// Copyright (c) 2010 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.
+
+// Trace events to track application performance.  Events consist of a name
+// a type (BEGIN, END or INSTANT), a tracking id and extra string data.
+// In addition, the current process id, thread id, a timestamp down to the
+// microsecond and a file and line number of the calling location.
+//
+// The current implementation logs these events into a log file of the form
+// trace_<pid>.log where it's designed to be post-processed to generate a
+// trace report.  In the future, it may use another mechansim to facilitate
+// real-time analysis.
+
+#ifndef BASE_DEBUG_TRACE_EVENT_H_
+#define BASE_DEBUG_TRACE_EVENT_H_
+#pragma once
+
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+// On Windows we always pull in an alternative implementation
+// which logs to Event Tracing for Windows.
+//
+// Note that the Windows implementation is always enabled, irrespective the
+// value of the CHROMIUM_ENABLE_TRACE_EVENT define. The Windows implementation
+// is controlled by Event Tracing for Windows, which will turn tracing on only
+// if there is someone listening for the events it generates.
+#include "base/debug/trace_event_win.h"
+#else  // defined(OS_WIN)
+
+#include <string>
+
+#include "base/lock.h"
+#include "base/scoped_ptr.h"
+#include "base/singleton.h"
+#include "base/time.h"
+#include "base/timer.h"
+
+#ifndef CHROMIUM_ENABLE_TRACE_EVENT
+#define TRACE_EVENT_BEGIN(name, id, extra) ((void) 0)
+#define TRACE_EVENT_END(name, id, extra) ((void) 0)
+#define TRACE_EVENT_INSTANT(name, id, extra) ((void) 0)
+
+#else  // CHROMIUM_ENABLE_TRACE_EVENT
+// Use the following macros rather than using the TraceLog class directly as the
+// underlying implementation may change in the future.  Here's a sample usage:
+// TRACE_EVENT_BEGIN("v8.run", documentId, scriptLocation);
+// RunScript(script);
+// TRACE_EVENT_END("v8.run", documentId, scriptLocation);
+
+// Record that an event (of name, id) has begun.  All BEGIN events should have
+// corresponding END events with a matching (name, id).
+#define TRACE_EVENT_BEGIN(name, id, extra) \
+  Singleton<base::debug::TraceLog>::get()->Trace( \
+      name, \
+      base::debug::TraceLog::EVENT_BEGIN, \
+      reinterpret_cast<const void*>(id), \
+      extra, \
+      __FILE__, \
+      __LINE__)
+
+// Record that an event (of name, id) has ended.  All END events should have
+// corresponding BEGIN events with a matching (name, id).
+#define TRACE_EVENT_END(name, id, extra) \
+  Singleton<base::debug::TraceLog>::get()->Trace( \
+      name, \
+      base::debug::TraceLog::EVENT_END, \
+      reinterpret_cast<const void*>(id), \
+      extra, \
+      __FILE__, \
+      __LINE__)
+
+// Record that an event (of name, id) with no duration has happened.
+#define TRACE_EVENT_INSTANT(name, id, extra) \
+  Singleton<base::debug::TraceLog>::get()->Trace( \
+      name, \
+      base::debug::TraceLog::EVENT_INSTANT, \
+      reinterpret_cast<const void*>(id), \
+      extra, \
+      __FILE__, \
+      __LINE__)
+#endif  // CHROMIUM_ENABLE_TRACE_EVENT
+
+namespace base {
+
+class ProcessMetrics;
+
+namespace debug {
+
+class TraceLog {
+ public:
+  enum EventType {
+    EVENT_BEGIN,
+    EVENT_END,
+    EVENT_INSTANT
+  };
+
+  // Is tracing currently enabled.
+  static bool IsTracing();
+  // Start logging trace events.
+  static bool StartTracing();
+  // Stop logging trace events.
+  static void StopTracing();
+
+  // Log a trace event of (name, type, id) with the optional extra string.
+  void Trace(const std::string& name,
+             EventType type,
+             const void* id,
+             const std::wstring& extra,
+             const char* file,
+             int line);
+  void Trace(const std::string& name,
+             EventType type,
+             const void* id,
+             const std::string& extra,
+             const char* file,
+             int line);
+
+ private:
+  // This allows constructor and destructor to be private and usable only
+  // by the Singleton class.
+  friend struct DefaultSingletonTraits<TraceLog>;
+
+  TraceLog();
+  ~TraceLog();
+  bool OpenLogFile();
+  void CloseLogFile();
+  bool Start();
+  void Stop();
+  void Heartbeat();
+  void Log(const std::string& msg);
+
+  bool enabled_;
+  FILE* log_file_;
+  Lock file_lock_;
+  TimeTicks trace_start_time_;
+#ifndef ANDROID
+  scoped_ptr<base::ProcessMetrics> process_metrics_;
+#endif
+  RepeatingTimer<TraceLog> timer_;
+};
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // defined(OS_WIN)
+
+#endif  // BASE_DEBUG_TRACE_EVENT_H_