Add a HistogramRecorder class and use cases.

chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc

Index: chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
diff --git a/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc b/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
index 96405ad79cac69fa52bcc9bc678baf687c212f05..03596d6b3e5e9421537a2e6d1e3ae596e2193120 100644
--- a/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
+++ b/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
@@ -7,28 +7,30 @@
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
-#include "base/metrics/histogram.h"
 #include "base/metrics/histogram_samples.h"
-#include "base/metrics/statistics_recorder.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/histogram_recorder.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using base::HistogramBase;
-using base::HistogramSamples;
-using base::StatisticsRecorder;
-
 class SpellcheckHostMetricsTest : public testing::Test {
  public:
   SpellcheckHostMetricsTest() : loop_(base::MessageLoop::TYPE_DEFAULT) {
   }
 
   virtual void SetUp() OVERRIDE {
-    base::StatisticsRecorder::Initialize();
+    ResetHistogramRecorder();
     metrics_.reset(new SpellCheckHostMetrics);
   }
 
+  void ResetHistogramRecorder() {
+    histogram_recorder_.reset(new base::HistogramRecorder());
+  }
+
   SpellCheckHostMetrics* metrics() { return metrics_.get(); }
-  void RecordWordCountsForTesting() { metrics_->RecordWordCounts(); }
+  void RecordWordCountsForTesting() { metrics()->RecordWordCounts(); }
+
+ protected:
+  scoped_ptr<base::HistogramRecorder> histogram_recorder_;
 
  private:
   base::MessageLoop loop_;
@@ -36,52 +38,36 @@ class SpellcheckHostMetricsTest : public testing::Test {
 };
 
 TEST_F(SpellcheckHostMetricsTest, RecordEnabledStats) {
-  scoped_ptr<HistogramSamples> baseline;
-  HistogramBase* histogram =
-      StatisticsRecorder::FindHistogram("SpellCheck.Enabled");
-  if (histogram)
-    baseline = histogram->SnapshotSamples();
+  const char kMetricName[] = "SpellCheck.Enabled";
 
   metrics()->RecordEnabledStats(false);
 
-  histogram =
-      StatisticsRecorder::FindHistogram("SpellCheck.Enabled");
-  ASSERT_TRUE(histogram != NULL);
-  scoped_ptr<HistogramSamples> samples(histogram->SnapshotSamples());
-  if (baseline.get())
-    samples->Subtract(*baseline);
-  EXPECT_EQ(1, samples->GetCount(0));
-  EXPECT_EQ(0, samples->GetCount(1));
+  scoped_ptr<base::HistogramSamples> samples(
+      histogram_recorder_.get()->GetHistogramSamplesSinceCreation(kMetricName));
+  EXPECT_EQ(1, samples.get()->GetCount(0));
+  EXPECT_EQ(0, samples.get()->GetCount(1));
 
-  baseline.reset(samples.release());
+  ResetHistogramRecorder();
 
   metrics()->RecordEnabledStats(true);
 
-  histogram =
-      StatisticsRecorder::FindHistogram("SpellCheck.Enabled");
-  ASSERT_TRUE(histogram != NULL);
-  samples = histogram->SnapshotSamples();
-  samples->Subtract(*baseline);
-  EXPECT_EQ(0, samples->GetCount(0));
-  EXPECT_EQ(1, samples->GetCount(1));
+  samples =
+      histogram_recorder_.get()->GetHistogramSamplesSinceCreation(kMetricName);
+  EXPECT_EQ(0, samples.get()->GetCount(0));
+  EXPECT_EQ(1, samples.get()->GetCount(1));
 }
 
 TEST_F(SpellcheckHostMetricsTest, CustomWordStats) {
   SpellCheckHostMetrics::RecordCustomWordCountStats(123);
 
-  HistogramBase* histogram =
-      StatisticsRecorder::FindHistogram("SpellCheck.CustomWords");
-  ASSERT_TRUE(histogram != NULL);
-  scoped_ptr<HistogramSamples> baseline = histogram->SnapshotSamples();
+  ResetHistogramRecorder();
 
   SpellCheckHostMetrics::RecordCustomWordCountStats(23);
-  histogram =
-      StatisticsRecorder::FindHistogram("SpellCheck.CustomWords");
-  ASSERT_TRUE(histogram != NULL);
-  scoped_ptr<HistogramSamples> samples = histogram->SnapshotSamples();
 
-  samples->Subtract(*baseline);
-  EXPECT_EQ(23,samples->sum());
+  scoped_ptr<base::HistogramSamples> samples(
+      histogram_recorder_.get()->GetHistogramSamplesSinceCreation(
+          "SpellCheck.CustomWords"));
+  EXPECT_EQ(23, samples.get()->sum());
 }
 
 TEST_F(SpellcheckHostMetricsTest, RecordWordCountsDiscardsDuplicates) {
@@ -99,59 +85,37 @@ TEST_F(SpellcheckHostMetricsTest, RecordWordCountsDiscardsDuplicates) {
   metrics()->RecordCheckedWordStats(string16(ASCIIToUTF16("test")), false);
   RecordWordCountsForTesting();
 
-  // Get baselines for all affected histograms.
-  scoped_ptr<HistogramSamples> baselines[arraysize(histogramName)];
-  for (size_t i = 0; i < arraysize(histogramName); ++i) {
-    HistogramBase* histogram =
-        StatisticsRecorder::FindHistogram(histogramName[i]);
-    if (histogram)
-      baselines[i] = histogram->SnapshotSamples();
-  }
+  // Restart the recorder.
+  ResetHistogramRecorder();
 
   // Nothing changed, so this invocation should not affect any histograms.
   RecordWordCountsForTesting();
 
   // Get samples for all affected histograms.
-  scoped_ptr<HistogramSamples> samples[arraysize(histogramName)];
+  scoped_ptr<base::HistogramSamples> samples;
   for (size_t i = 0; i < arraysize(histogramName); ++i) {
-    HistogramBase* histogram =
-        StatisticsRecorder::FindHistogram(histogramName[i]);
-    ASSERT_TRUE(histogram != NULL);
-    samples[i] = histogram->SnapshotSamples();
-    if (baselines[i].get())
-      samples[i]->Subtract(*baselines[i]);
-
-    EXPECT_EQ(0, samples[i]->TotalCount());
+    samples = histogram_recorder_.get()->GetHistogramSamplesSinceCreation(
+        histogramName[i]);
+    EXPECT_EQ(0, samples.get()->TotalCount());
   }
 }
 
 TEST_F(SpellcheckHostMetricsTest, RecordSpellingServiceStats) {
   const char kMetricName[] = "SpellCheck.SpellingService.Enabled";
-  scoped_ptr<HistogramSamples> baseline;
-  HistogramBase* histogram = StatisticsRecorder::FindHistogram(kMetricName);
-  if (histogram)
-    baseline = histogram->SnapshotSamples();
 
   metrics()->RecordSpellingServiceStats(false);
 
-  histogram =
-      StatisticsRecorder::FindHistogram(kMetricName);
-  ASSERT_TRUE(histogram != NULL);
-  scoped_ptr<HistogramSamples> samples(histogram->SnapshotSamples());
-  if (baseline.get())
-    samples->Subtract(*baseline);
-  EXPECT_EQ(1, samples->GetCount(0));
-  EXPECT_EQ(0, samples->GetCount(1));
+  scoped_ptr<base::HistogramSamples> samples(
+      histogram_recorder_.get()->GetHistogramSamplesSinceCreation(kMetricName));
+  EXPECT_EQ(1, samples.get()->GetCount(0));
+  EXPECT_EQ(0, samples.get()->GetCount(1));
 
-  baseline.reset(samples.release());
+  ResetHistogramRecorder();
 
   metrics()->RecordSpellingServiceStats(true);
 
-  histogram =
-      StatisticsRecorder::FindHistogram(kMetricName);
-  ASSERT_TRUE(histogram != NULL);
-  samples = histogram->SnapshotSamples();
-  samples->Subtract(*baseline);
-  EXPECT_EQ(0, samples->GetCount(0));
-  EXPECT_EQ(1, samples->GetCount(1));
+  samples =
+      histogram_recorder_.get()->GetHistogramSamplesSinceCreation(kMetricName);
+  EXPECT_EQ(0, samples.get()->GetCount(0));
+  EXPECT_EQ(1, samples.get()->GetCount(1));
 }