Update from https://crrev.com/328418

base/prefs/json_pref_store_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/prefs/json_pref_store.h"
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
+#include "base/location.h"
 #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"
+#include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/simple_test_clock.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread.h"
 #include "base/values.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace {
 
 const char kHomePage[] = "homepage";
 
+// Set the time on the given SimpleTestClock to the given time in minutes.
+void SetCurrentTimeInMinutes(double minutes, base::SimpleTestClock* clock) {
+  const int32_t kBaseTimeMins = 100;
+  clock->SetNow(base::Time::FromDoubleT((kBaseTimeMins + minutes) * 60));
+}
+
 // A PrefFilter that will intercept all calls to FilterOnLoad() and hold on
 // to the |prefs| until explicitly asked to release them.
 class InterceptingPrefFilter : public PrefFilter {
  public:
   InterceptingPrefFilter();
   ~InterceptingPrefFilter() override;
 
   // PrefFilter implementation:
   void FilterOnLoad(
       const PostFilterOnLoadCallback& post_filter_on_load_callback,
@@ skipping 50 matching lines @@
     ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
 
     ASSERT_TRUE(PathService::Get(base::DIR_TEST_DATA, &data_dir_));
     data_dir_ = data_dir_.AppendASCII("prefs");
     ASSERT_TRUE(PathExists(data_dir_));
   }
 
   void TearDown() override {
     // Make sure all pending tasks have been processed (e.g., deleting the
     // JsonPrefStore may post write tasks).
-    message_loop_.PostTask(FROM_HERE, MessageLoop::QuitWhenIdleClosure());
+    message_loop_.task_runner()->PostTask(FROM_HERE,
+                                          MessageLoop::QuitWhenIdleClosure());
     message_loop_.Run();
   }
 
   // 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.
   base::FilePath data_dir_;
   // A message loop that we can use as the file thread message loop.
   MessageLoop message_loop_;
+
+ private:
+  // Ensure histograms are reset for each test.
+  StatisticsRecorder statistics_recorder_;
 };
 
 // Test fallback behavior for a nonexistent file.
 TEST_F(JsonPrefStoreTest, NonExistentFile) {
   base::FilePath bogus_input_file = data_dir_.AppendASCII("read.txt");
   ASSERT_FALSE(PathExists(bogus_input_file));
   scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      bogus_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+      bogus_input_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
   EXPECT_EQ(PersistentPrefStore::PREF_READ_ERROR_NO_FILE,
             pref_store->ReadPrefs());
   EXPECT_FALSE(pref_store->ReadOnly());
 }
 
 // Test fallback behavior for a nonexistent file and alternate file.
 TEST_F(JsonPrefStoreTest, NonExistentFileAndAlternateFile) {
   base::FilePath bogus_input_file = data_dir_.AppendASCII("read.txt");
   base::FilePath bogus_alternate_input_file =
       data_dir_.AppendASCII("read_alternate.txt");
   ASSERT_FALSE(PathExists(bogus_input_file));
   ASSERT_FALSE(PathExists(bogus_alternate_input_file));
-  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      bogus_input_file,
-      bogus_alternate_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+  scoped_refptr<JsonPrefStore> pref_store =
+      new JsonPrefStore(bogus_input_file, bogus_alternate_input_file,
+                        message_loop_.task_runner(), scoped_ptr<PrefFilter>());
   EXPECT_EQ(PersistentPrefStore::PREF_READ_ERROR_NO_FILE,
             pref_store->ReadPrefs());
   EXPECT_FALSE(pref_store->ReadOnly());
 }
 
 // Test fallback behavior for an invalid file.
 TEST_F(JsonPrefStoreTest, InvalidFile) {
   base::FilePath invalid_file_original = data_dir_.AppendASCII("invalid.json");
   base::FilePath invalid_file = temp_dir_.path().AppendASCII("invalid.json");
   ASSERT_TRUE(base::CopyFile(invalid_file_original, invalid_file));
-  scoped_refptr<JsonPrefStore> pref_store =
-      new JsonPrefStore(invalid_file,
-                        message_loop_.message_loop_proxy().get(),
-                        scoped_ptr<PrefFilter>());
+  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
+      invalid_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
   EXPECT_EQ(PersistentPrefStore::PREF_READ_ERROR_JSON_PARSE,
             pref_store->ReadPrefs());
   EXPECT_FALSE(pref_store->ReadOnly());
 
   // The file should have been moved aside.
   EXPECT_FALSE(PathExists(invalid_file));
   base::FilePath moved_aside = temp_dir_.path().AppendASCII("invalid.bad");
   EXPECT_TRUE(PathExists(moved_aside));
   EXPECT_TRUE(TextContentsEqual(invalid_file_original, moved_aside));
 }
@@ skipping 65 matching lines @@
 }
 
 TEST_F(JsonPrefStoreTest, Basic) {
   ASSERT_TRUE(base::CopyFile(data_dir_.AppendASCII("read.json"),
                              temp_dir_.path().AppendASCII("write.json")));
 
   // Test that the persistent value can be loaded.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   ASSERT_TRUE(PathExists(input_file));
   scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+      input_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
   ASSERT_EQ(PersistentPrefStore::PREF_READ_ERROR_NONE, pref_store->ReadPrefs());
   EXPECT_FALSE(pref_store->ReadOnly());
   EXPECT_TRUE(pref_store->IsInitializationComplete());
 
   // The JSON file looks like this:
   // {
   //   "homepage": "http://www.cnn.com",
   //   "some_directory": "/usr/local/",
   //   "tabs": {
   //     "new_windows_in_tabs": true,
   //     "max_tabs": 20
   //   }
   // }
 
   RunBasicJsonPrefStoreTest(
       pref_store.get(), input_file, data_dir_.AppendASCII("write.golden.json"));
 }
 
 TEST_F(JsonPrefStoreTest, BasicAsync) {
   ASSERT_TRUE(base::CopyFile(data_dir_.AppendASCII("read.json"),
                              temp_dir_.path().AppendASCII("write.json")));
 
   // Test that the persistent value can be loaded.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   ASSERT_TRUE(PathExists(input_file));
   scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+      input_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   {
     MockPrefStoreObserver mock_observer;
     pref_store->AddObserver(&mock_observer);
 
     MockReadErrorDelegate* mock_error_delegate = new MockReadErrorDelegate;
     pref_store->ReadPrefsAsync(mock_error_delegate);
 
     EXPECT_CALL(mock_observer, OnInitializationCompleted(true)).Times(1);
     EXPECT_CALL(*mock_error_delegate,
@@ skipping 16 matching lines @@
   // }
 
   RunBasicJsonPrefStoreTest(
       pref_store.get(), input_file, data_dir_.AppendASCII("write.golden.json"));
 }
 
 TEST_F(JsonPrefStoreTest, PreserveEmptyValues) {
   FilePath pref_file = temp_dir_.path().AppendASCII("empty_values.json");
 
   scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      pref_file,
-      message_loop_.message_loop_proxy(),
-      scoped_ptr<PrefFilter>());
+      pref_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   // Set some keys with empty values.
   pref_store->SetValue("list", new base::ListValue);
   pref_store->SetValue("dict", new base::DictionaryValue);
 
   // Write to file.
   pref_store->CommitPendingWrite();
   MessageLoop::current()->RunUntilIdle();
 
   // Reload.
-  pref_store = new JsonPrefStore(
-      pref_file,
-      message_loop_.message_loop_proxy(),
-      scoped_ptr<PrefFilter>());
+  pref_store = new JsonPrefStore(pref_file, message_loop_.task_runner(),
+                                 scoped_ptr<PrefFilter>());
   ASSERT_EQ(PersistentPrefStore::PREF_READ_ERROR_NONE, pref_store->ReadPrefs());
   ASSERT_FALSE(pref_store->ReadOnly());
 
   // Check values.
   const Value* result = NULL;
   EXPECT_TRUE(pref_store->GetValue("list", &result));
   EXPECT_TRUE(ListValue().Equals(result));
   EXPECT_TRUE(pref_store->GetValue("dict", &result));
   EXPECT_TRUE(DictionaryValue().Equals(result));
 }
 
 // This test is just documenting some potentially non-obvious behavior. It
 // shouldn't be taken as normative.
 TEST_F(JsonPrefStoreTest, RemoveClearsEmptyParent) {
   FilePath pref_file = temp_dir_.path().AppendASCII("empty_values.json");
 
   scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      pref_file,
-      message_loop_.message_loop_proxy(),
-      scoped_ptr<PrefFilter>());
+      pref_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   base::DictionaryValue* dict = new base::DictionaryValue;
   dict->SetString("key", "value");
   pref_store->SetValue("dict", dict);
 
   pref_store->RemoveValue("dict.key");
 
   const base::Value* retrieved_dict = NULL;
   bool has_dict = pref_store->GetValue("dict", &retrieved_dict);
   EXPECT_FALSE(has_dict);
 }
 
 // Tests asynchronous reading of the file when there is no file.
 TEST_F(JsonPrefStoreTest, AsyncNonExistingFile) {
   base::FilePath bogus_input_file = data_dir_.AppendASCII("read.txt");
   ASSERT_FALSE(PathExists(bogus_input_file));
   scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      bogus_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+      bogus_input_file, message_loop_.task_runner(), scoped_ptr<PrefFilter>());
   MockPrefStoreObserver mock_observer;
   pref_store->AddObserver(&mock_observer);
 
   MockReadErrorDelegate *mock_error_delegate = new MockReadErrorDelegate;
   pref_store->ReadPrefsAsync(mock_error_delegate);
 
   EXPECT_CALL(mock_observer, OnInitializationCompleted(true)).Times(1);
   EXPECT_CALL(*mock_error_delegate,
               OnError(PersistentPrefStore::PREF_READ_ERROR_NO_FILE)).Times(1);
   RunLoop().RunUntilIdle();
   pref_store->RemoveObserver(&mock_observer);
 
   EXPECT_FALSE(pref_store->ReadOnly());
 }
 
 TEST_F(JsonPrefStoreTest, ReadWithInterceptor) {
   ASSERT_TRUE(base::CopyFile(data_dir_.AppendASCII("read.json"),
                              temp_dir_.path().AppendASCII("write.json")));
 
   // Test that the persistent value can be loaded.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   ASSERT_TRUE(PathExists(input_file));
 
   scoped_ptr<InterceptingPrefFilter> intercepting_pref_filter(
       new InterceptingPrefFilter());
   InterceptingPrefFilter* raw_intercepting_pref_filter_ =
       intercepting_pref_filter.get();
-  scoped_refptr<JsonPrefStore> pref_store =
-      new JsonPrefStore(input_file,
-                        message_loop_.message_loop_proxy().get(),
-                        intercepting_pref_filter.Pass());
+  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
+      input_file, message_loop_.task_runner(), intercepting_pref_filter.Pass());
 
   ASSERT_EQ(PersistentPrefStore::PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE,
             pref_store->ReadPrefs());
   EXPECT_FALSE(pref_store->ReadOnly());
 
   // The store shouldn't be considered initialized until the interceptor
   // returns.
   EXPECT_TRUE(raw_intercepting_pref_filter_->has_intercepted_prefs());
   EXPECT_FALSE(pref_store->IsInitializationComplete());
   EXPECT_FALSE(pref_store->GetValue(kHomePage, NULL));
@@ skipping 23 matching lines @@
                              temp_dir_.path().AppendASCII("write.json")));
 
   // Test that the persistent value can be loaded.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   ASSERT_TRUE(PathExists(input_file));
 
   scoped_ptr<InterceptingPrefFilter> intercepting_pref_filter(
       new InterceptingPrefFilter());
   InterceptingPrefFilter* raw_intercepting_pref_filter_ =
       intercepting_pref_filter.get();
-  scoped_refptr<JsonPrefStore> pref_store =
-      new JsonPrefStore(input_file,
-                        message_loop_.message_loop_proxy().get(),
-                        intercepting_pref_filter.Pass());
+  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
+      input_file, message_loop_.task_runner(), intercepting_pref_filter.Pass());
 
   MockPrefStoreObserver mock_observer;
   pref_store->AddObserver(&mock_observer);
 
   // Ownership of the |mock_error_delegate| is handed to the |pref_store| below.
   MockReadErrorDelegate* mock_error_delegate = new MockReadErrorDelegate;
 
   {
     pref_store->ReadPrefsAsync(mock_error_delegate);
 
@@ skipping 42 matching lines @@
       base::CopyFile(data_dir_.AppendASCII("read.json"),
                      temp_dir_.path().AppendASCII("alternate.json")));
 
   // Test that the alternate file is moved to the main file and read as-is from
   // there.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   base::FilePath alternate_input_file =
       temp_dir_.path().AppendASCII("alternate.json");
   ASSERT_FALSE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
-  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      input_file,
-      alternate_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+  scoped_refptr<JsonPrefStore> pref_store =
+      new JsonPrefStore(input_file, alternate_input_file,
+                        message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   ASSERT_FALSE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
   ASSERT_EQ(PersistentPrefStore::PREF_READ_ERROR_NONE, pref_store->ReadPrefs());
 
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_FALSE(PathExists(alternate_input_file));
 
   EXPECT_FALSE(pref_store->ReadOnly());
   EXPECT_TRUE(pref_store->IsInitializationComplete());
@@ skipping 21 matching lines @@
                      temp_dir_.path().AppendASCII("alternate.json")));
 
   // Test that the alternate file is ignored and that the read occurs from the
   // existing main file. There is no attempt at even deleting the alternate
   // file as this scenario should never happen in normal user-data-dirs.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   base::FilePath alternate_input_file =
       temp_dir_.path().AppendASCII("alternate.json");
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
-  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      input_file,
-      alternate_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+  scoped_refptr<JsonPrefStore> pref_store =
+      new JsonPrefStore(input_file, alternate_input_file,
+                        message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
   ASSERT_EQ(PersistentPrefStore::PREF_READ_ERROR_NONE, pref_store->ReadPrefs());
 
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
 
   EXPECT_FALSE(pref_store->ReadOnly());
   EXPECT_TRUE(pref_store->IsInitializationComplete());
@@ skipping 17 matching lines @@
       base::CopyFile(data_dir_.AppendASCII("read.json"),
                      temp_dir_.path().AppendASCII("write.json")));
 
   // Test that the basic read works fine when an alternate file is specified but
   // does not exist.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   base::FilePath alternate_input_file =
       temp_dir_.path().AppendASCII("alternate.json");
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_FALSE(PathExists(alternate_input_file));
-  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      input_file,
-      alternate_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+  scoped_refptr<JsonPrefStore> pref_store =
+      new JsonPrefStore(input_file, alternate_input_file,
+                        message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_FALSE(PathExists(alternate_input_file));
   ASSERT_EQ(PersistentPrefStore::PREF_READ_ERROR_NONE, pref_store->ReadPrefs());
 
   ASSERT_TRUE(PathExists(input_file));
   ASSERT_FALSE(PathExists(alternate_input_file));
 
   EXPECT_FALSE(pref_store->ReadOnly());
   EXPECT_TRUE(pref_store->IsInitializationComplete());
@@ skipping 17 matching lines @@
       base::CopyFile(data_dir_.AppendASCII("read.json"),
                      temp_dir_.path().AppendASCII("alternate.json")));
 
   // Test that the alternate file is moved to the main file and read as-is from
   // there even when the read is made asynchronously.
   base::FilePath input_file = temp_dir_.path().AppendASCII("write.json");
   base::FilePath alternate_input_file =
       temp_dir_.path().AppendASCII("alternate.json");
   ASSERT_FALSE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
-  scoped_refptr<JsonPrefStore> pref_store = new JsonPrefStore(
-      input_file,
-      alternate_input_file,
-      message_loop_.message_loop_proxy().get(),
-      scoped_ptr<PrefFilter>());
+  scoped_refptr<JsonPrefStore> pref_store =
+      new JsonPrefStore(input_file, alternate_input_file,
+                        message_loop_.task_runner(), scoped_ptr<PrefFilter>());
 
   ASSERT_FALSE(PathExists(input_file));
   ASSERT_TRUE(PathExists(alternate_input_file));
 
   {
     MockPrefStoreObserver mock_observer;
     pref_store->AddObserver(&mock_observer);
 
     MockReadErrorDelegate* mock_error_delegate = new MockReadErrorDelegate;
     pref_store->ReadPrefsAsync(mock_error_delegate);
@@ skipping 18 matching lines @@
   //   "tabs": {
   //     "new_windows_in_tabs": true,
   //     "max_tabs": 20
   //   }
   // }
 
   RunBasicJsonPrefStoreTest(
       pref_store.get(), input_file, data_dir_.AppendASCII("write.golden.json"));
 }
 
+TEST_F(JsonPrefStoreTest, WriteCountHistogramTestBasic) {
+  SimpleTestClock* test_clock = new SimpleTestClock;
+  SetCurrentTimeInMinutes(0, test_clock);
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      scoped_ptr<base::Clock>(test_clock));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  histogram.RecordWriteOccured();
+
+  SetCurrentTimeInMinutes(1.5 * report_interval, test_clock);
+  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) {
+  SimpleTestClock* test_clock = new SimpleTestClock;
+  SetCurrentTimeInMinutes(0, test_clock);
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      scoped_ptr<base::Clock>(test_clock));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.5 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.7 * report_interval, test_clock);
+  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, test_clock);
+  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, test_clock);
+  histogram.ReportOutstandingWrites();
+
+  samples = histogram.GetHistogram()->SnapshotSamples();
+  ASSERT_EQ(1, samples->GetCount(3));
+  ASSERT_EQ(1, samples->TotalCount());
+}
+
+TEST_F(JsonPrefStoreTest, WriteCountHistogramTestMultiplePeriods) {
+  SimpleTestClock* test_clock = new SimpleTestClock;
+  SetCurrentTimeInMinutes(0, test_clock);
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      scoped_ptr<base::Clock>(test_clock));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.5 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(0.7 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(1.3 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(1.5 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(2.1 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(2.5 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(2.7 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(3.3 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+
+  // The last write won't be recorded because the second count period hasn't
+  // fully elapsed
+  SetCurrentTimeInMinutes(3.5 * report_interval, test_clock);
+  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) {
+  SimpleTestClock* test_clock = new SimpleTestClock;
+  SetCurrentTimeInMinutes(0, test_clock);
+  JsonPrefStore::WriteCountHistogram histogram(
+      base::TimeDelta::FromSeconds(10),
+      base::FilePath(FILE_PATH_LITERAL("/tmp/Local State")),
+      scoped_ptr<base::Clock>(test_clock));
+  int32 report_interval =
+      JsonPrefStore::WriteCountHistogram::kHistogramWriteReportIntervalMins;
+
+  // 1 write in the first period.
+  histogram.RecordWriteOccured();
+
+  // No writes in the second and third periods.
+
+  // 2 writes in the fourth period.
+  SetCurrentTimeInMinutes(3.1 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(3.3 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+
+  // No writes in the fifth period.
+
+  // 3 writes in the sixth period.
+  SetCurrentTimeInMinutes(5.1 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(5.3 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+  SetCurrentTimeInMinutes(5.5 * report_interval, test_clock);
+  histogram.RecordWriteOccured();
+
+  SetCurrentTimeInMinutes(6.1 * report_interval, test_clock);
+  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