[Sync] Convert NonBlockingDataTypeController to be single-thread.

components/sync/driver/non_ui_model_type_controller_unittest.cc

Index: components/sync/driver/non_ui_model_type_controller_unittest.cc
diff --git a/components/sync/driver/non_ui_model_type_controller_unittest.cc b/components/sync/driver/non_ui_model_type_controller_unittest.cc
index 5d67af937791843dfef7a7c2844b4564d26eb668..a18e1fcceddb9e3f1b5f6fd7890dc0da37b87e21 100644
--- a/components/sync/driver/non_ui_model_type_controller_unittest.cc
+++ b/components/sync/driver/non_ui_model_type_controller_unittest.cc
@@ -170,9 +170,9 @@ class NonUIModelTypeControllerTest : public testing::Test,
     RunQueuedUIThreadTasks();
   }
 
-  syncer_v2::ModelTypeService* GetModelTypeServiceForType(
+  base::WeakPtr<syncer_v2::ModelTypeService> GetModelTypeServiceForType(
       syncer::ModelType type) override {
-    return service_.get();
+    return service_->AsWeakPtr();
   }
 
  protected: