[Sync] Add a sanity integration test for USS.

components/browser_sync/browser/profile_sync_components_factory_impl.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 "components/browser_sync/browser/profile_sync_components_factory_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
@@ skipping 243 matching lines @@
   // disabled.
   if (!disabled_types.Has(syncer::PASSWORDS)) {
     sync_service->RegisterDataTypeController(
         base::MakeUnique<PasswordDataTypeController>(
             error_callback, sync_client_,
             sync_client_->GetPasswordStateChangedCallback(), password_store_));
   }
 
   if (!disabled_types.Has(syncer::PREFERENCES) &&
       base::FeatureList::IsEnabled(kSyncPreferencesFeature)) {
-    sync_service->RegisterDataTypeController(
-        base::MakeUnique<UIDataTypeController>(syncer::PREFERENCES,
-                                               error_callback, sync_client_));
+    if (!override_prefs_controller_to_uss_for_test_) {
+      sync_service->RegisterDataTypeController(
+          base::MakeUnique<UIDataTypeController>(syncer::PREFERENCES,
+                                                 error_callback, sync_client_));
+    } else {
+      sync_service->RegisterDataTypeController(
+          base::MakeUnique<UIModelTypeController>(
+              syncer::PREFERENCES, error_callback, sync_client_));
+    }
   }
 
   if (!disabled_types.Has(syncer::PRIORITY_PREFERENCES)) {
     sync_service->RegisterDataTypeController(
         base::MakeUnique<UIDataTypeController>(syncer::PRIORITY_PREFERENCES,
                                                error_callback, sync_client_));
   }
 
   // Article sync is disabled by default.  Register only if explicitly enabled.
   if (dom_distiller::IsEnableSyncArticlesSet()) {
@@ skipping 129 matching lines @@
   const bool kExpectMobileBookmarksFolder = false;
 #endif
   BookmarkModelAssociator* model_associator = new BookmarkModelAssociator(
       bookmark_model, sync_service->GetSyncClient(), user_share,
       error_handler->Copy(), kExpectMobileBookmarksFolder);
   BookmarkChangeProcessor* change_processor =
       new BookmarkChangeProcessor(sync_service->GetSyncClient(),
                                   model_associator, std::move(error_handler));
   return SyncComponents(model_associator, change_processor);
 }
+
+// static
+void ProfileSyncComponentsFactoryImpl::OverridePrefsForUssTest(bool use_uss) {
+  override_prefs_controller_to_uss_for_test_ = use_uss;
+}
+
+bool ProfileSyncComponentsFactoryImpl::
+    override_prefs_controller_to_uss_for_test_ = false;