base/test/histogram_tester.h: Add a way to query a whole family of related

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 96317f98d2d33283ed09a8d3e69487312af1dd38..8178abb5806d77c6811d23d790aca2aa8216fd0a 100644
--- a/base/test/histogram_tester.h
+++ b/base/test/histogram_tester.h
@@ -47,6 +47,25 @@ class HistogramTester {
   void ExpectTotalCount(const std::string& name,
                         base::HistogramBase::Count count) const;
 
+  // Finds histograms whose names start with |query|, and return a text

[Ilya Sherman, 2015/06/23 00:57:40]

nit: "return" -> "returns"

+  // representation of any new samples added since the creation of this object.
+  // Histograms that are unchanged are omitted from the result. The return value
+  // consists of lines of the form:
+  //
+  //   - "My.Statistic.Name[2]=5" (for linear, boolean, and enum histograms)
+  //   - "My.Statistic.Name=5"    (for other kinds of histograms)
+  //
+  // In the above example, 2 is the bucket min and 5 is the count. For nonlinear
+  // histograms, only the total across all buckets is shown, under the
+  // assumption that the inputs to nonlinear histograms -- sizes and times,
+  // commonly -- may be hard for a test to predict.
+  //
+  // 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_EQ, which does a
+  // good job of formatting human-readable diffs of multi-line strings.

[Ilya Sherman, 2015/06/23 00:57:40]

nit: You should probably mention somewhere that the returned list is sorted
alphabetically.

+  std::string GetTotalCountsForQuery(const std::string& query) const;
+
   // Access a modified HistogramSamples containing only what has been logged
   // to the histogram since the creation of this object.
   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(