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

base/metrics/histogram.cc

Index: base/metrics/histogram.cc
diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index 7ff1b16184f10c9e54dd501b1b95a1f34fefc253..152a1b8c3170efd58fa0869498c775ab50be2af9 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -284,6 +284,20 @@ void Histogram::Add(int value) {
   FindAndRunCallback(value);
 }
 
+void Histogram::MultiAdd(int value, int count) {

[Alexei Svitkine (slow), 2015/07/31 15:39:27]

We should disallow negative values.

[amohammadkhan, 2015/08/03 17:30:43]

Done. I change negative values to zero. Is it good enough or I have to make an
assertion or something else?

+  DCHECK_EQ(0, ranges(0));
+  DCHECK_EQ(kSampleType_MAX, ranges(bucket_count()));
+
+  if (value > kSampleType_MAX - 1)
+    value = kSampleType_MAX - 1;
+  if (value < 0)
+    value = 0;

[Alexei Svitkine (slow), 2015/07/31 15:39:27]

Can you make a helper function for this clamping in the anon namespace and use
it both here and in Add().

[amohammadkhan, 2015/08/03 17:30:43]

Done.

+  samples_->Accumulate(value, count);
+
+  FindAndRunCallback(value);
+

[Alexei Svitkine (slow), 2015/07/31 15:39:27]

Nit: Remove empty line.

[amohammadkhan, 2015/08/03 17:30:43]

Done.

+}
+
 scoped_ptr<HistogramSamples> Histogram::SnapshotSamples() const {
   return SnapshotSampleVector().Pass();
 }