Adding UseCounter specific for extensions

base/test/histogram_tester.h

 // Copyright 2014 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.
 
 #ifndef BASE_TEST_HISTOGRAM_TESTER_H_
 #define BASE_TEST_HISTOGRAM_TESTER_H_
 
 #include <map>
 #include <memory>
 #include <ostream>
@@ skipping 60 matching lines @@
   // If you build the expected list programmatically, you can use ContainerEq:
   //   EXPECT_THAT(histogram_tester.GetAllSamples("HistogramName"),
   //               ContainerEq(expected_buckets));
   //
   // or EXPECT_EQ if you prefer not to depend on gMock, at the expense of a
   // slightly less helpful failure message:
   //   EXPECT_EQ(expected_buckets,
   //             histogram_tester.GetAllSamples("HistogramName"));
   std::vector<Bucket> GetAllSamples(const std::string& name) const;
 
+  // Returns the value of the |sample| bucket for ths histogram |name|.
+  HistogramBase::Count GetBucketCount(const std::string& name,
+                                      HistogramBase::Sample sample) const;
+
   // Finds histograms whose names start with |prefix|, and returns them along
   // with the counts of any samples added since the creation of this object.
   // Histograms that are unchanged are omitted from the result. The return value
   // is a map whose keys are the histogram name, and whose values are the sample
   // count.
   //
   // This is useful for cases where the code under test is choosing among a
   // family of related histograms and incrementing one of them. Typically you
   // should pass the result of this function directly to EXPECT_THAT.
   //
@@ skipping 21 matching lines @@
                         Histogram::Count expected_count,
                         const HistogramSamples& samples) const;
 
   // Verifies that the total number of values recorded for the histogram |name|
   // is |expected_count|. This is checked against |samples| minus the snapshot
   // that was taken for |name|.
   void CheckTotalCount(const std::string& name,
                        Histogram::Count expected_count,
                        const HistogramSamples& samples) const;
 
+  // Sets the value for |count| to be the value in the |sample| bucket. The
+  // bucket's current value is determined from |samples| and is modified based
+  // on the snapshot stored for histogram |name|.
+  void GetBucketCountForSamples(const std::string& name,
+                                HistogramBase::Sample sample,
+                                const HistogramSamples& samples,
+                                HistogramBase::Count* count) const;
+
   // Used to determine the histogram changes made during this instance's
   // lifecycle.
   std::map<std::string, std::unique_ptr<HistogramSamples>> histograms_snapshot_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramTester);
 };
 
 struct Bucket {
   Bucket(HistogramBase::Sample min, HistogramBase::Count count)
       : min(min), count(count) {}
 
   bool operator==(const Bucket& other) const;
 
   HistogramBase::Sample min;
   HistogramBase::Count count;
 };
 
 void PrintTo(const Bucket& value, std::ostream* os);
 
 }  // namespace base
 
 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_