Add support to increase a UMA histogram bucket by an aribitrary integer.

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 58bc0297aba45c9838fe22ed8949880288c7edea..809e477b15d8eb38cb55b31205618e6a8847b254 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -181,6 +181,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
                                 Sample expected_maximum,
                                 size_t expected_bucket_count) const override;
   void Add(Sample value) override;
+  void MultiAdd(Sample value, int count) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const override;
   void AddSamples(const HistogramSamples& samples) override;
   bool AddSamplesFromPickle(base::PickleIterator* iter) override;
@@ -218,6 +219,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptBucketBounds);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptSampleCounts);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, NameMatchTest);
+  FRIEND_TEST_ALL_PREFIXES(HistogramTest, MultiAddTest);
 
   friend class StatisticsRecorder;  // To allow it to delete duplicates.
   friend class StatisticsRecorderTest;