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

histograms at once.

Use this to clean up site_isolation_stats_gatherer_browsertest.cc

BUG=481066

Review URL: https://codereview.chromium.org/1190423006

Cr-Commit-Position: refs/heads/master@{#340510}

2 files changed, 52 insertions, 8 deletions

diff --git a/base/test/histogram_tester.cc b/base/test/histogram_tester.cc
index 0eba3a9..0bff2f8 100644
--- a/base/test/histogram_tester.cc
+++ b/base/test/histogram_tester.cc
@@ -73,7 +73,8 @@ void HistogramTester::ExpectTotalCount(const std::string& name,
   }
 }
 
-std::vector<Bucket> HistogramTester::GetAllSamples(const std::string& name) {
+std::vector<Bucket> HistogramTester::GetAllSamples(
+    const std::string& name) const {
   std::vector<Bucket> samples;
   scoped_ptr<HistogramSamples> snapshot =
       GetHistogramSamplesSinceCreation(name);
@@ -86,16 +87,37 @@ std::vector<Bucket> HistogramTester::GetAllSamples(const std::string& name) {
   return samples;
 }
 
+HistogramTester::CountsMap HistogramTester::GetTotalCountsForPrefix(
+    const std::string& query) const {
+  EXPECT_TRUE(query.find('.') != std::string::npos)
+      << "|query| ought to contain at least one period, to avoid matching too"
+      << " many histograms.";
+
+  // Find matches by using the prefix-matching logic built into GetSnapshot().
+  StatisticsRecorder::Histograms query_matches;
+  StatisticsRecorder::GetSnapshot(query, &query_matches);
+
+  CountsMap result;
+  for (base::HistogramBase* histogram : query_matches) {
+    scoped_ptr<HistogramSamples> new_samples =
+        GetHistogramSamplesSinceCreation(histogram->histogram_name());
+    // Omit unchanged histograms from the result.
+    if (new_samples->TotalCount()) {
+      result[histogram->histogram_name()] = new_samples->TotalCount();
+    }
+  }
+  return result;
+}
+
 scoped_ptr<HistogramSamples> HistogramTester::GetHistogramSamplesSinceCreation(
-    const std::string& histogram_name) {
+    const std::string& histogram_name) const {
   HistogramBase* histogram = StatisticsRecorder::FindHistogram(histogram_name);
   if (!histogram)
     return scoped_ptr<HistogramSamples>();
   scoped_ptr<HistogramSamples> named_samples(histogram->SnapshotSamples());
-  HistogramSamples* named_original_samples =
-      histograms_snapshot_[histogram_name];
-  if (named_original_samples)
-    named_samples->Subtract(*named_original_samples);
+  auto original_samples_it = histograms_snapshot_.find(histogram_name);
+  if (original_samples_it != histograms_snapshot_.end())
+    named_samples->Subtract(*original_samples_it->second);
   return named_samples.Pass();
 }
 
diff --git a/base/test/histogram_tester.h b/base/test/histogram_tester.h
index 7ac7ca6..cfab3c6 100644
--- a/base/test/histogram_tester.h
+++ b/base/test/histogram_tester.h
@@ -26,6 +26,8 @@ class HistogramSamples;
 // getting logged as intended.
 class HistogramTester {
  public:
+  using CountsMap = std::map<std::string, base::HistogramBase::Count>;
+
   // The constructor will call StatisticsRecorder::Initialize() for you. Also,
   // this takes a snapshot of all current histograms counts.
   HistogramTester();
@@ -67,12 +69,32 @@ class HistogramTester {
   // slightly less helpful failure message:
   //   EXPECT_EQ(expected_buckets,
   //             histogram_tester.GetAllSamples("HistogramName"));
-  std::vector<Bucket> GetAllSamples(const std::string& name);
+  std::vector<Bucket> GetAllSamples(const std::string& name) const;
+
+  // Finds histograms whose names start with |query|, 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.
+  //
+  // Example usage, using gmock (which produces better failure messages):
+  //   #include "testing/gmock/include/gmock/gmock.h"
+  // ...
+  //   base::HistogramTester::CountsMap expected_counts;
+  //   expected_counts["MyMetric.A"] = 1;
+  //   expected_counts["MyMetric.B"] = 1;
+  //   EXPECT_THAT(histogram_tester.GetTotalCountsForPrefix("MyMetric."),
+  //               testing::ContainerEq(expected_counts));
+  CountsMap GetTotalCountsForPrefix(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(
-      const std::string& histogram_name);
+      const std::string& histogram_name) const;
 
  private:
   // Verifies and asserts that value in the |sample| bucket matches the