Reorganize histograms for persistence.

base/metrics/sparse_histogram.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.
 
 #ifndef BASE_METRICS_SPARSE_HISTOGRAM_H_
 #define BASE_METRICS_SPARSE_HISTOGRAM_H_
 
 #include <map>
 #include <string>
 
@@ skipping 19 matching lines @@
 
 class BASE_EXPORT SparseHistogram : public HistogramBase {
  public:
   // If there's one with same name, return the existing one. If not, create a
   // new one.
   static HistogramBase* FactoryGet(const std::string& name, int32 flags);
 
   ~SparseHistogram() override;
 
   // HistogramBase implementation:
+  uint64_t name_hash() const override;
   HistogramType GetHistogramType() const override;
   bool HasConstructionArguments(Sample expected_minimum,
                                 Sample expected_maximum,
                                 size_t expected_bucket_count) const override;
   void Add(Sample value) override;
   void AddCount(Sample value, int count) override;
   void AddSamples(const HistogramSamples& samples) override;
   bool AddSamplesFromPickle(base::PickleIterator* iter) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const override;
   void WriteHTMLGraph(std::string* output) const override;
@@ skipping 32 matching lines @@
   mutable base::Lock lock_;
 
   SampleMap samples_;
 
   DISALLOW_COPY_AND_ASSIGN(SparseHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_SPARSE_HISTOGRAM_H_