Use TimeTicks as much as possible in startup_metric_utils.

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"
@@ skipping 32 matching lines @@
 
  private:
   friend struct base::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_;
+  // Keeps track of the TimeTicks at which each initialization phase was

[msw, 2015/11/10 18:58:38]

nit: the comment change isn't really necessary.

[gab, 2015/11/10 19:18:49]

Done.

+  // reached.
+  std::map<Location, base::TimeTicks> profiled_ticks_;
 
   // 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_