[Sync] Register USS types with ModelTypeRegistry before download

components/sync_driver/directory_data_type_controller.h

Index: components/sync_driver/directory_data_type_controller.h
diff --git a/components/sync_driver/directory_data_type_controller.h b/components/sync_driver/directory_data_type_controller.h
index bf68edad8792ada2afffe7a179fa7104d8a38e46..41311fdb1c026203952a3dadaa7e49f457e38b62 100644
--- a/components/sync_driver/directory_data_type_controller.h
+++ b/components/sync_driver/directory_data_type_controller.h
@@ -18,6 +18,11 @@ class DirectoryDataTypeController : public DataTypeController {
   // DataTypeController implementation.
   bool ShouldLoadModelBeforeConfigure() const override;
 
+  // Directory based data types don't need to register with backend.
+  // ModelTypeRegistry will create all necessary objects in
+  // SetEnabledDirectoryTypes based on routing info.
+  void RegisterWithBackend(BackendDataTypeConfigurer* configurer) override;
+
   // Directory specific implementation of ActivateDataType with the
   // type specific ChangeProcessor and ModelSafeGroup.
   // Activates change processing on the controlled data type.