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

base/metrics/sparse_histogram.h

Index: base/metrics/sparse_histogram.h
diff --git a/base/metrics/sparse_histogram.h b/base/metrics/sparse_histogram.h
index a02da592d6f59599508307701b47449d43656133..e6ef12c1cc30069d549d0a82f93d16397a4245a3 100644
--- a/base/metrics/sparse_histogram.h
+++ b/base/metrics/sparse_histogram.h
@@ -42,6 +42,7 @@ class BASE_EXPORT_PRIVATE SparseHistogram : public HistogramBase {
                                 Sample expected_maximum,
                                 size_t expected_bucket_count) const override;
   void Add(Sample value) override;
+  void MultiAdd (Sample value, int repetition) override;
   void AddSamples(const HistogramSamples& samples) override;
   bool AddSamplesFromPickle(base::PickleIterator* iter) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const override;