Add Statistics for SupervisedUserSettingService during merging and syncing data.

chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service_unittest.cc

Index: chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service_unittest.cc
diff --git a/chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service_unittest.cc b/chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service_unittest.cc
index e7b0675550bc3431854fd4d9eb927d68564d4b38..f2afb87a4ed59e2822d8d6a4475a7ed865203fde 100644
--- a/chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service_unittest.cc
+++ b/chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service_unittest.cc
@@ -87,7 +87,7 @@ class SupervisedUserSharedSettingsServiceTest : public ::testing::Test {
       : settings_service_(profile_.GetPrefs()) {}
   ~SupervisedUserSharedSettingsServiceTest() override {}
 
-  void StartSyncing(const syncer::SyncDataList& initial_sync_data) {
+  SyncMergeResult StartSyncing(const syncer::SyncDataList& initial_sync_data) {
     sync_processor_.reset(new syncer::FakeSyncChangeProcessor);
     scoped_ptr<syncer::SyncErrorFactory> error_handler(
         new MockSyncErrorFactory(SUPERVISED_USER_SHARED_SETTINGS));
@@ -97,6 +97,7 @@ class SupervisedUserSharedSettingsServiceTest : public ::testing::Test {
             new SyncChangeProcessorWrapperForTest(sync_processor_.get())),
         std::move(error_handler));
     EXPECT_FALSE(result.error().IsSet());
+    return result;
   }
 
   const base::DictionaryValue* GetAllSettings() {
@@ -190,7 +191,12 @@ TEST_F(SupervisedUserSharedSettingsServiceTest, SetAndGet) {
 
 TEST_F(SupervisedUserSharedSettingsServiceTest, Merge) {
   // Set initial values, then stop syncing so we can restart.
-  StartSyncing(SyncDataList());
+  SyncMergeResult result = StartSyncing(SyncDataList());
+  EXPECT_EQ(0, result.num_items_added());
+  EXPECT_EQ(0, result.num_items_deleted());
+  EXPECT_EQ(0, result.num_items_modified());
+  EXPECT_EQ(0, result.num_items_before_association());
+  EXPECT_EQ(0, result.num_items_after_association());
 
   const char kIdA[] = "aaaaaa";
   const char kIdB[] = "bbbbbb";
@@ -214,7 +220,14 @@ TEST_F(SupervisedUserSharedSettingsServiceTest, Merge) {
       SupervisedUserSharedSettingsService::CreateSyncDataForSetting(
           kIdC, "baz", blurp, true));
 
-  StartSyncing(sync_data);
+  result = StartSyncing(sync_data);
+
+  EXPECT_EQ(1, result.num_items_added());
+  EXPECT_EQ(0, result.num_items_deleted());
+  EXPECT_EQ(1, result.num_items_modified());
+  EXPECT_EQ(3, result.num_items_before_association());
+  EXPECT_EQ(4, result.num_items_after_association());
+
   EXPECT_EQ(2u, sync_processor_->changes().size());
   VerifySyncChangesAndClear();
   EXPECT_EQ(2u, changed_settings_.size());