[Sync] Use ModelError all the way through to ModelTypeController.

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 350b055c799237c001ca4ba4a117ebbc6ef31ea1..b4b2777894bfe0a1917aba93752286f1a84be48e 100644
--- a/components/sync/driver/directory_data_type_controller.h
+++ b/components/sync/driver/directory_data_type_controller.h
@@ -59,6 +59,9 @@ class DirectoryDataTypeController : public DataTypeController {
                               SyncClient* sync_client,
                               ModelSafeGroup model_safe_group);
 
+  // Create an error handler that reports back to this controller.
+  virtual std::unique_ptr<DataTypeErrorHandler> CreateErrorHandler() = 0;
+
   // Access to the ChangeProcessor for the type being controlled by |this|.
   // Returns null if the ChangeProcessor isn't created or connected.
   virtual ChangeProcessor* GetChangeProcessor() const = 0;