Add histograms to record the number of writes to the prefs file

base/prefs/json_pref_store_unittest.cc

Index: base/prefs/json_pref_store_unittest.cc
diff --git a/base/prefs/json_pref_store_unittest.cc b/base/prefs/json_pref_store_unittest.cc
index ff68836014f65bcb780e8aac035224e79a61d655..37406670139734600057d849162d0e535a2e4e29 100644
--- a/base/prefs/json_pref_store_unittest.cc
+++ b/base/prefs/json_pref_store_unittest.cc
@@ -10,6 +10,8 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram_samples.h"
+#include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/prefs/pref_filter.h"
 #include "base/run_loop.h"
@@ -85,6 +87,14 @@ class MockReadErrorDelegate : public PersistentPrefStore::ReadErrorDelegate {
 }  // namespace
 
 class JsonPrefStoreTest : public testing::Test {
+ public:
+  base::Time current_time() { return current_time_; }
+
+  void SetCurrentTimeInMinutes(double minutes) {
+    const int32_t kBaseTimeMins = 100;
+    current_time_ = base::Time::FromDoubleT((kBaseTimeMins + minutes) * 60);
+  }
+
  protected:
   void SetUp() override {
     ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
@@ -92,6 +102,9 @@ class JsonPrefStoreTest : public testing::Test {
     ASSERT_TRUE(PathService::Get(base::DIR_TEST_DATA, &data_dir_));
     data_dir_ = data_dir_.AppendASCII("prefs");
     ASSERT_TRUE(PathExists(data_dir_));
+
+    base::StatisticsRecorder::InitializeForTest();
+    SetCurrentTimeInMinutes(0);
   }
 
   void TearDown() override {
@@ -101,6 +114,8 @@ class JsonPrefStoreTest : public testing::Test {
     message_loop_.Run();
   }
 
+  base::Time current_time_;
+
   // The path to temporary directory used to contain the test operations.
   base::ScopedTempDir temp_dir_;
   // The path to the directory where the test data is stored.
@@ -671,4 +686,144 @@ TEST_F(JsonPrefStoreTest, BasicAsyncWithAlternateFile) {
       pref_store.get(), input_file, data_dir_.AppendASCII("write.golden.json"));
 }
 
+TEST_F(JsonPrefStoreTest, WriteCountHistogramTestBasic) {
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      base::Bind(&JsonPrefStoreTest::current_time, base::Unretained(this)));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  SetCurrentTimeInMinutes(0);
+  histogram.RecordWriteOccured();
+
+  SetCurrentTimeInMinutes(1.5 * report_interval);
+  histogram.ReportOutstandingWrites();
+  scoped_ptr<HistogramSamples> samples =
+      histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(1, samples->GetCount(1));
+  ASSERT_EQ(1, samples->TotalCount());
+
+  ASSERT_EQ("Settings.JsonDataWriteCount.Local_State",
+            histogram.GetHistogram()->histogram_name());
+  ASSERT_TRUE(histogram.GetHistogram()->HasConstructionArguments(1, 30, 31));
+}
+
+TEST_F(JsonPrefStoreTest, WriteCountHistogramTestSinglePeriod) {
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      base::Bind(&JsonPrefStoreTest::current_time, base::Unretained(this)));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  SetCurrentTimeInMinutes(0);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.5 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.7 * report_interval);
+  histogram.RecordWriteOccured();
+
+  // Nothing should be recorded until the report period has elapsed.
+  scoped_ptr<HistogramSamples> samples =
+      histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(0, samples->TotalCount());
+
+  SetCurrentTimeInMinutes(1.3 * report_interval);
+  histogram.RecordWriteOccured();
+
+  // Now the report period has elapsed.
+  samples = histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(1, samples->GetCount(3));
+  ASSERT_EQ(1, samples->TotalCount());
+
+  // The last write won't be recorded because the second count period hasn't
+  // fully elapsed.
+  SetCurrentTimeInMinutes(1.5 * report_interval);
+  histogram.ReportOutstandingWrites();
+
+  samples = histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(1, samples->GetCount(3));
+  ASSERT_EQ(1, samples->TotalCount());
+}
+
+TEST_F(JsonPrefStoreTest, WriteCountHistogramTestMultiplePeriods) {
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      base::Bind(&JsonPrefStoreTest::current_time, base::Unretained(this)));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  SetCurrentTimeInMinutes(0);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.5 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.7 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(1.3 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(1.5 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(2.1 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(2.5 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(2.7 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(3.3 * report_interval);
+  histogram.RecordWriteOccured();
+
+  // The last write won't be recorded because the second count period hasn't
+  // fully elapsed
+  SetCurrentTimeInMinutes(3.5 * report_interval);
+  histogram.ReportOutstandingWrites();
+  scoped_ptr<HistogramSamples> samples =
+      histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(2, samples->GetCount(3));
+  ASSERT_EQ(1, samples->GetCount(2));
+  ASSERT_EQ(3, samples->TotalCount());
+}
+
+TEST_F(JsonPrefStoreTest, WriteCountHistogramTestPeriodWithGaps) {
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      base::Bind(&JsonPrefStoreTest::current_time, base::Unretained(this)));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  // 1 write in the first period.
+  SetCurrentTimeInMinutes(0);
+  histogram.RecordWriteOccured();
+
+  // No writes in the second and third periods.
+
+  // 2 writes in the fourth period.
+  SetCurrentTimeInMinutes(3.1 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(3.3 * report_interval);
+  histogram.RecordWriteOccured();
+
+  // No writes in the fifth period.
+
+  // 3 writes in the sixth period.
+  SetCurrentTimeInMinutes(5.1 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(5.3 * report_interval);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(5.5 * report_interval);
+  histogram.RecordWriteOccured();
+
+  SetCurrentTimeInMinutes(6.1 * report_interval);
+  histogram.ReportOutstandingWrites();
+  scoped_ptr<HistogramSamples> samples =
+      histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(3, samples->GetCount(0));
+  ASSERT_EQ(1, samples->GetCount(1));
+  ASSERT_EQ(1, samples->GetCount(2));
+  ASSERT_EQ(1, samples->GetCount(3));
+  ASSERT_EQ(6, samples->TotalCount());
+}
+
 }  // namespace base