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

base/metrics/histogram_unittest.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/histogram.h"
 
 #include <climits>
 #include <algorithm>
 #include <vector>
 
@@ skipping 213 matching lines @@
   Histogram* histogram = static_cast<Histogram*>(
       CustomHistogram::FactoryGet("2BucketsCustomHistogram", custom_ranges,
                                   HistogramBase::kNoFlags));
   const BucketRanges* ranges = histogram->bucket_ranges();
   ASSERT_EQ(3u, ranges->size());
   EXPECT_EQ(0, ranges->range(0));
   EXPECT_EQ(4, ranges->range(1));
   EXPECT_EQ(HistogramBase::kSampleType_MAX, ranges->range(2));
 }
 
+// Test the AddCount function.
+TEST_F(HistogramTest, AddCountTest) {
+  const size_t kBucketCount = 50;
+  Histogram* histogram = static_cast<Histogram*>(
+      Histogram::FactoryGet("AddCountHistogram", 10, 100, kBucketCount,
+                            HistogramBase::kNoFlags));
+
+  histogram->AddCount(20, 15);
+  histogram->AddCount(30, 14);
+
+  scoped_ptr<SampleVector> samples = histogram->SnapshotSampleVector();
+  EXPECT_EQ(29, samples->TotalCount());
+  EXPECT_EQ(15, samples->GetCount(20));
+  EXPECT_EQ(14, samples->GetCount(30));
+
+  histogram->AddCount(20, 25);
+  histogram->AddCount(30, 24);
+
+  scoped_ptr<SampleVector> samples2 = histogram->SnapshotSampleVector();
+  EXPECT_EQ(78, samples2->TotalCount());
+  EXPECT_EQ(40, samples2->GetCount(20));
+  EXPECT_EQ(38, samples2->GetCount(30));
+}
+
 // Make sure histogram handles out-of-bounds data gracefully.
 TEST_F(HistogramTest, BoundsTest) {
   const size_t kBucketCount = 50;
   Histogram* histogram = static_cast<Histogram*>(
       Histogram::FactoryGet("Bounded", 10, 100, kBucketCount,
                             HistogramBase::kNoFlags));
 
   // Put two samples "out of bounds" above and below.
   histogram->Add(5);
   histogram->Add(-50);
@@ skipping 259 matching lines @@
   // CustomHistogram needs at least 1 valid range.
   custom_ranges.clear();
   custom_ranges.push_back(0);
   EXPECT_DEATH(CustomHistogram::FactoryGet("BadRangesCustom3", custom_ranges,
                                            HistogramBase::kNoFlags),
                "");
 }
 #endif
 
 }  // namespace base