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

base/metrics/sparse_histogram.cc

Index: base/metrics/sparse_histogram.cc
diff --git a/base/metrics/sparse_histogram.cc b/base/metrics/sparse_histogram.cc
index a853dce3505f450c5ef814371f63f1fa92e7523f..39c276d7877290a9a93123b728061cb06099c51b 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -46,9 +46,17 @@ bool SparseHistogram::HasConstructionArguments(
 }
 
 void SparseHistogram::Add(Sample value) {
+  AddCount(value, 1);
+}
+
+void SparseHistogram::AddCount(Sample value, int count) {
+  if (count <= 0) {
+    NOTREACHED();
+    return;
+  }
   {
     base::AutoLock auto_lock(lock_);
-    samples_.Accumulate(value, 1);
+    samples_.Accumulate(value, count);
   }
 
   FindAndRunCallback(value);