[Sync] USS: Fix race condition in DeviceInfoService + add error handling

sync/api/fake_model_type_change_processor.h

Index: sync/api/fake_model_type_change_processor.h
diff --git a/sync/api/fake_model_type_change_processor.h b/sync/api/fake_model_type_change_processor.h
index 4d31f4d2469e788c0fa10d9e05e4fff25902d8d1..4bf59b6d33b0146c533c0a592d09079f8272003c 100644
--- a/sync/api/fake_model_type_change_processor.h
+++ b/sync/api/fake_model_type_change_processor.h
@@ -36,6 +36,9 @@ class FakeModelTypeChangeProcessor : public ModelTypeChangeProcessor {
   void OnSyncStarting(syncer::DataTypeErrorHandler* error_handler,
                       const StartCallback& callback) override;
   void DisableSync() override;
+  syncer::SyncError CreateAndUploadError(
+      const tracked_objects::Location& location,
+      const std::string& message) override;
 };
 
 }  // namespace syncer_v2