Improve UMA tests; improve no-op reconcilor; new reconcilor test.

base/test/statistics_delta_reader.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 BASE_TEST_STATISTICS_DELTA_READER_H_
 #define BASE_TEST_STATISTICS_DELTA_READER_H_
 
 #include <map>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 
 class HistogramSamples;
 
 // This class acts as a differential reader for histogram samples, enabling
 // tests to check that metrics were recorded as they should be.
+//
+// This class is DEPRECATED.
+// TODO(mlerman): Remove all references to this class with UMAHistogramHelper
+// references. crbug.com/384011

[Ilya Sherman, 2014/06/13 19:58:11]

This class is actually used from //net, which cannot depend on a helper class
defined in //chrome/test/base.  So, FYI, as part of reconciling these two
classes, you'll want to move the helper class into //base/test, same as where
this file lives.

[Mike Lerman, 2014/06/16 14:59:13]

I may, although there is code in UMAHistogramHelper which needs to live within
Chrome. This class is only referenced once within //net, so I may just make that
a special case... but that conversation can happen in the other bug :)

 class StatisticsDeltaReader {
  public:
   StatisticsDeltaReader();
   ~StatisticsDeltaReader();
 
   // Returns the histogram data accumulated since this instance was created.
   // Returns NULL if no samples are available.
   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
       const std::string& histogram_name);
 
  private:
   // Used to determine the histogram changes made during this instance's
   // lifecycle. This instance takes ownership of the samples, which are deleted
   // when the instance is destroyed.
   std::map<std::string, HistogramSamples*> original_samples_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsDeltaReader);
 };
 
 }  // namespace base
 
 #endif  // BASE_TEST_STATISTICS_DELTA_READER_H_