Merge multiple histogram snapshots into single one for reporting.

base/metrics/sample_map.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.
 
 // SampleMap implements HistogramSamples interface. It is used by the
 // SparseHistogram class to store samples.
 
 #ifndef BASE_METRICS_SAMPLE_MAP_H_
 #define BASE_METRICS_SAMPLE_MAP_H_
 
@@ skipping 10 matching lines @@
  public:
   SampleMap();
   explicit SampleMap(uint64 id);
   ~SampleMap() override;
 
   // HistogramSamples implementation:
   void Accumulate(HistogramBase::Sample value,
                   HistogramBase::Count count) override;
   HistogramBase::Count GetCount(HistogramBase::Sample value) const override;
   HistogramBase::Count TotalCount() const override;
+  void Negate() override;
   scoped_ptr<SampleCountIterator> Iterator() const override;
 
  protected:
   bool AddSubtractImpl(
       SampleCountIterator* iter,
       HistogramSamples::Operator op) override;  // |op| is ADD or SUBTRACT.
 
  private:
   std::map<HistogramBase::Sample, HistogramBase::Count> sample_counts_;
 
@@ skipping 18 matching lines @@
  private:
   void SkipEmptyBuckets();
 
   SampleToCountMap::const_iterator iter_;
   const SampleToCountMap::const_iterator end_;
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_SAMPLE_MAP_H_