Adding UseCounter specific for extensions

base/test/histogram_tester.h

Index: base/test/histogram_tester.h
diff --git a/base/test/histogram_tester.h b/base/test/histogram_tester.h
index ecf33f831f0d1844531821a5face3c01ff30b198..682e8f6b9bf8735b8e2883f02e4e9d0617f4501f 100644
--- a/base/test/histogram_tester.h
+++ b/base/test/histogram_tester.h
@@ -54,6 +54,12 @@ class HistogramTester {
   void ExpectTotalCount(const std::string& name,
                         HistogramBase::Count count) const;
 
+  // This tests total count of a given histogram, excluding one bucket, given
+  // the sample id.
+  void ExpectTotalCountExcept(const std::string& name,
+                              HistogramBase::Sample sample,

[Nico, 2017/05/09 19:36:46]

s/sample/except/

[lunalu1, 2017/05/10 19:39:38]

Done.

+                              HistogramBase::Count count) const;
+
   // We know exact number of samples for buckets corresponding to a time
   // interval. Other intervals may have samples too.
   void ExpectTimeBucketCount(const std::string& name,
@@ -119,6 +125,16 @@ class HistogramTester {
                        Histogram::Count expected_count,
                        const HistogramSamples& samples) const;
 
+  // Verifies that the total number of values recorded for the histogram |name|,
+  // excluding the value in the |sample| bucket, matches the |expected_count|.
+  // The histogram's current total counts and its bucket's current value is
+  // determined from |samples| and is modified based on the snapshot restored
+  // for histogram |name|.

[Alexei Svitkine (slow), 2017/05/10 15:17:30]

I wonder if it wouldn't be better to just have functions to get the total counts
and the counts for the buckets and do this testing in the caller?

[lunalu1, 2017/05/10 19:39:38]

That was my initial thought. But after seeing that no other getters were
implemented, I decided to write a tester instead (thinking that this might be
what the owner would like to keep). But I could totally write 2 callers instead.

[Alexei Svitkine (slow), 2017/05/10 19:45:19]

I agree that it would be different with how the class is currently designed, but
I think it would be a positive change. The current design comes with some
downsides - specifically if you have multiple calls to this, you won't know
which one failed since the file/line number you'll get is from within the helper
class and not the test.

I think it's fine to introduce getters in this CL and do the tests outside the
class - sure it will create an inconsistency but I think it's better than adding
very custom Check functions that are only used from a single place.

+  void CheckTotalCountExcept(const std::string& name,
+                             HistogramBase::Sample sample,

[Nico, 2017/05/09 19:36:46]

I'd s/sample/except/ here too

[lunalu1, 2017/05/10 19:39:38]

Done.

+                             Histogram::Count expected_count,
+                             const HistogramSamples& samples) const;
+
   // Used to determine the histogram changes made during this instance's
   // lifecycle.
   std::map<std::string, std::unique_ptr<HistogramSamples>> histograms_snapshot_;