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

base/metrics/sparse_histogram.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/sparse_histogram.h"
 
 #include "base/metrics/sample_map.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/pickle.h"
 #include "base/strings/stringprintf.h"
@@ skipping 28 matching lines @@
 
 bool SparseHistogram::HasConstructionArguments(
     Sample expected_minimum,
     Sample expected_maximum,
     size_t expected_bucket_count) const {
   // SparseHistogram never has min/max/bucket_count limit.
   return false;
 }
 
 void SparseHistogram::Add(Sample value) {
+  AddCount(value, 1);
+}
+
+void SparseHistogram::AddCount(Sample value, int count) {
   {
     base::AutoLock auto_lock(lock_);
-    samples_.Accumulate(value, 1);
+    if (count < 0) {

[Alexei Svitkine (slow), 2015/08/03 18:15:42]

Same comment as in the other method. This if can probably be at the start of the
method, before the lock.

[amohammadkhan, 2015/08/04 18:22:51]

Done.

+      count = 0;
+    }
+    samples_.Accumulate(value, count);
   }
-

[Alexei Svitkine (slow), 2015/08/03 18:15:42]

Nit: Keep the empty line.

[amohammadkhan, 2015/08/04 18:22:51]

Done.

   FindAndRunCallback(value);
 }
 
 scoped_ptr<HistogramSamples> SparseHistogram::SnapshotSamples() const {
   scoped_ptr<SampleMap> snapshot(new SampleMap());
 
   base::AutoLock auto_lock(lock_);
   snapshot->Add(samples_);
   return snapshot.Pass();
 }
@@ skipping 106 matching lines @@
                                        std::string* output) const {
   StringAppendF(output,
                 "Histogram: %s recorded %d samples",
                 histogram_name().c_str(),
                 total_count);
   if (flags() & ~kHexRangePrintingFlag)
     StringAppendF(output, " (flags = 0x%x)", flags() & ~kHexRangePrintingFlag);
 }
 
 }  // namespace base