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

base/metrics/histogram_base.h

Index: base/metrics/histogram_base.h
diff --git a/base/metrics/histogram_base.h b/base/metrics/histogram_base.h
index 1bc1f6eb6fe78bf4a48576f60e3da694a74da932..820ac3b8be870158febdd801ebac545d8a970669 100644
--- a/base/metrics/histogram_base.h
+++ b/base/metrics/histogram_base.h
@@ -120,6 +120,7 @@ class BASE_EXPORT HistogramBase {
                                         size_t expected_bucket_count) const = 0;
 
   virtual void Add(Sample value) = 0;
+  virtual void MultiAdd(Sample value, int repetition) = 0;
 
   // 2 convenient functions that call Add(Sample).
   void AddTime(const TimeDelta& time);