Remove some dead code about "acknowledged types"

components/sync_driver/sync_prefs_unittest.cc

Index: components/sync_driver/sync_prefs_unittest.cc
diff --git a/components/sync_driver/sync_prefs_unittest.cc b/components/sync_driver/sync_prefs_unittest.cc
index b1f34235ce20b804d60032c83b7655abcc3a0ebd..bcfbc7b32b7ad0980f267c9cf21f8caafaff1526 100644
--- a/components/sync_driver/sync_prefs_unittest.cc
+++ b/components/sync_driver/sync_prefs_unittest.cc
@@ -201,21 +201,6 @@ TEST_F(SyncPrefsTest, ObservedPrefs) {
   sync_prefs.RemoveSyncPrefObserver(&mock_sync_pref_observer);
 }
 
-TEST_F(SyncPrefsTest, AcknowledgeSyncedTypes) {
-  SyncPrefs sync_prefs(&pref_service_);
-
-  syncer::ModelTypeSet expected_acknowledge_synced_types =
-      sync_prefs.GetAcknowledgeSyncedTypesForTest();
-  for (int i = syncer::EXTENSION_SETTINGS; i < syncer::MODEL_TYPE_COUNT; ++i) {
-    const syncer::ModelType type = syncer::ModelTypeFromInt(i);
-    syncer::ModelTypeSet acknowledge_synced_types(type);
-    expected_acknowledge_synced_types.Put(type);
-    sync_prefs.AcknowledgeSyncedTypes(acknowledge_synced_types);
-    EXPECT_TRUE(expected_acknowledge_synced_types.Equals(
-        sync_prefs.GetAcknowledgeSyncedTypesForTest()));
-  }
-}
-
 TEST_F(SyncPrefsTest, ClearPreferences) {
   SyncPrefs sync_prefs(&pref_service_);