Add histograms to record the number of writes to the prefs file

base/metrics/statistics_recorder.h

 // Copyright (c) 2012 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.
 
 // StatisticsRecorder holds all Histograms and BucketRanges that are used by
 // Histograms in the system. It provides a general place for
 // Histograms/BucketRanges to register, and supports a global API for accessing
 // (i.e., dumping, or graphing) the data.
 
 #ifndef BASE_METRICS_STATISTICS_RECORDER_H_
@@ skipping 15 matching lines @@
 class HistogramBase;
 class Lock;
 
 class BASE_EXPORT StatisticsRecorder {
  public:
   typedef std::vector<HistogramBase*> Histograms;
 
   // Initializes the StatisticsRecorder system. Safe to call multiple times.
   static void Initialize();
 
+  // Reset the StatisticsRecorder system for testing. All existing histogram

[Alexei Svitkine (slow), 2015/04/27 20:21:20]

Nit: Reset -> Resets

To be consistent with the docs for the function above. (Even though I realise
the rest of the file is not consistent.)

[raymes, 2015/04/28 00:32:57]

Done.

+  // data will be erased.
+  static void ResetForTesting();
+
   // Find out if histograms can now be registered into our list.
   static bool IsActive();
 
   // Register, or add a new histogram to the collection of statistics. If an
   // identically named histogram is already registered, then the argument
   // |histogram| will deleted.  The returned value is always the registered
   // histogram (either the argument, or the pre-existing registered histogram).
   static HistogramBase* RegisterOrDeleteDuplicate(HistogramBase* histogram);
 
   // Register, or add a new BucketRanges. If an identically BucketRanges is
@@ skipping 60 matching lines @@
 
   // Lock protects access to above maps.
   static base::Lock* lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_