[Spellcheck] Add UMA stat for SpellingService

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 a2b9bb3c2c2a77d2c78ea76f2d490011a5b20365..8614d53f203bd6555002839873b517a3aa8ca04f 100644
--- a/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
+++ b/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
@@ -124,3 +124,35 @@ TEST_F(SpellcheckHostMetricsTest, RecordWordCountsDiscardsDuplicates) {
     EXPECT_EQ(0, samples[i]->TotalCount());
   }
 }
+
+TEST_F(SpellcheckHostMetricsTest, RecordSpellingServiceStats) {
+  const char kMetricName[] = "SpellCheck.SpellingService.Enabled";
+  scoped_ptr<HistogramSamples> baseline;
+  Histogram* histogram =
+      StatisticsRecorder::FindHistogram(kMetricName);
+  if (histogram)

[rpetterson, 2013/02/21 22:01:06]

When would this not be here? Or rather, why use "if" as opposed to ASSERT?

[groby-ooo-7-16, 2013/02/22 04:32:29]

If no counts for this histogram have been recorded yet, histogram will be NULL.
This happens _only_ if this is the very first test accessing the stat.
Unfortunately, histogram state can't be easily reset and survives until the
process gets shut down.  If _any_ other unit tests added to that histogram, we
get a non-NULL pointer.

That means both cases are valid, hence no ASSERT.

+    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));
+
+  baseline.reset(samples.release());
+
+  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));
+}