Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram_samples.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_HISTOGRAM_SAMPLES_H_
 #define BASE_METRICS_HISTOGRAM_SAMPLES_H_
 
 #include "base/atomicops.h"
 #include "base/basictypes.h"
 #include "base/metrics/histogram_base.h"
@@ skipping 37 matching lines @@
 
   explicit HistogramSamples(uint64 id);
   HistogramSamples(uint64 id, Metadata* meta);
   virtual ~HistogramSamples();
 
   virtual void Accumulate(HistogramBase::Sample value,
                           HistogramBase::Count count) = 0;
   virtual HistogramBase::Count GetCount(HistogramBase::Sample value) const = 0;
   virtual HistogramBase::Count TotalCount() const = 0;
 
+  virtual void Negate() = 0;
   virtual void Add(const HistogramSamples& other);
 
   // Add from serialized samples.
   virtual bool AddFromPickle(PickleIterator* iter);
 
   virtual void Subtract(const HistogramSamples& other);
 
   virtual scoped_ptr<SampleCountIterator> Iterator() const = 0;
   virtual bool Serialize(Pickle* pickle) const;
 
@@ skipping 38 matching lines @@
 
   // Get the index of current histogram bucket.
   // For histograms that don't use predefined buckets, it returns false.
   // Requires: !Done();
   virtual bool GetBucketIndex(size_t* index) const;
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_SAMPLES_H_