mac: Add a profiler for startup time.

chrome/browser/mac/mac_startup_profiler.h

+// 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,
+  };
+
+  // This method should be called at the earliest convenient time after Chrome
+  // has launched.
+  void RecordLaunchTime();

[jeremy, 2014/07/17 11:10:18]

Can you remove this and instead use the timestamp calculated in
startup_metric_utils::MainEntryPointTimeInternal() ?

That way our startup stats will be comparable to each ohter.

[erikchen, 2014/07/17 18:14:06]

Done.

+
+  // Saves the current time for later processing.

[jeremy, 2014/07/17 11:10:18]

nit: this comment isn't very clear, how about something like:

Record timestamp for the given location event ?

[erikchen, 2014/07/17 18:14:06]

Used your suggested comment.

+  void Profile(Location location);
+
+  // Records UMA metrics from all profiled locations.
+  void RecordMetrics();

[jeremy, 2014/07/17 11:10:18]

nit:
// Call once to record all UMA metrics for all profiled locations ?

[erikchen, 2014/07/17 18:14:06]

Used your suggested comment.

+
+ 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_;
+
+  // The time at which Chrome was launched.
+  base::Time launch_time_;
+
+  DISALLOW_COPY_AND_ASSIGN(MacStartupProfiler);
+};
+
+#endif  // CHROME_BROWSER_MAC_MAC_STARTUP_PROFILER_H_