[Sync] Add a sanity integration test for USS.

components/browser_sync/browser/profile_sync_components_factory_impl.cc

Index: components/browser_sync/browser/profile_sync_components_factory_impl.cc
diff --git a/components/browser_sync/browser/profile_sync_components_factory_impl.cc b/components/browser_sync/browser/profile_sync_components_factory_impl.cc
index a96b1ee316a87c30d338d15631f9a877aa4d3bb8..c905756263a539a9bc48b6d905080cbe0189bde0 100644
--- a/components/browser_sync/browser/profile_sync_components_factory_impl.cc
+++ b/components/browser_sync/browser/profile_sync_components_factory_impl.cc
@@ -261,9 +261,15 @@ void ProfileSyncComponentsFactoryImpl::RegisterCommonDataTypes(
 
   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_for_uss_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)) {
@@ -413,3 +419,10 @@ ProfileSyncComponentsFactoryImpl::CreateBookmarkSyncComponents(
                                   model_associator, std::move(error_handler));
   return SyncComponents(model_associator, change_processor);
 }
+
+// static
+void ProfileSyncComponentsFactoryImpl::OverridePrefsForUssTest() {
+  override_prefs_for_uss_test_ = true;
+}
+
+bool ProfileSyncComponentsFactoryImpl::override_prefs_for_uss_test_ = false;

[skym, 2016/09/12 19:57:50]

Why not do this assignment in the .h file?

[maxbogue, 2016/09/13 03:44:54]

Can't :(