mac: Add a profiler for startup time.

chrome/browser/mac/mac_startup_profiler.h

Index: chrome/browser/mac/mac_startup_profiler.h
diff --git a/chrome/browser/mac/mac_startup_profiler.h b/chrome/browser/mac/mac_startup_profiler.h
new file mode 100644
index 0000000000000000000000000000000000000000..f4e560cd7fc832d82bbd02bee57d5d1437372465
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+++ b/chrome/browser/mac/mac_startup_profiler.h
@@ -0,0 +1,62 @@
+// Copyright 2014 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 CHROME_BROWSER_MAC_MAC_STARTUP_PROFILER_H_
+#define CHROME_BROWSER_MAC_MAC_STARTUP_PROFILER_H_
+
+#include <map>
+
+#include "base/memory/singleton.h"
+#include "base/time/time.h"
+
+// A lightweight profiler of startup performance. Records UMA metrics for the
+// time delta between Chrome's launch and major initialization phases.
+class MacStartupProfiler {
+ public:
+  // Returns pointer to the singleton instance for the current process.
+  static MacStartupProfiler* GetInstance();
+
+  MacStartupProfiler();
+  ~MacStartupProfiler();
+
+  // These locations correspond to major phases of Chrome startup.
+  // Profiling of these locations should occur at the beginning of the method
+  // indicated by the enum name.
+  // The ordering of the enum matches the order in which the initialization
+  // phases are reached.
+  enum Location {
+    PRE_MAIN_MESSAGE_LOOP_START,
+    AWAKE_FROM_NIB,
+    POST_MAIN_MESSAGE_LOOP_START,
+    PRE_PROFILE_INIT,
+    POST_PROFILE_INIT,
+    WILL_FINISH_LAUNCHING,
+    DID_FINISH_LAUNCHING,
+  };
+
+  // Record timestamp for the given location event.
+  void Profile(Location location);
+
+  // Call once to record all UMA metrics for all profiled locations.
+  void RecordMetrics();
+
+ private:
+  friend struct DefaultSingletonTraits<MacStartupProfiler>;
+
+  // Returns the name of the histogram for the given location.
+  const std::string HistogramName(Location location);
+
+  // Records UMA metrics for a specific location.
+  void RecordHistogram(Location location, const base::TimeDelta& delta);
+
+  // Keeps track of the time at which each initialization phase was reached.
+  std::map<Location, base::Time> profiled_times_;
+
+  // Whether UMA metrics have been recorded. Only record UMA metrics once.
+  bool recorded_metrics_;
+
+  DISALLOW_COPY_AND_ASSIGN(MacStartupProfiler);
+};
+
+#endif  // CHROME_BROWSER_MAC_MAC_STARTUP_PROFILER_H_