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

components/sync/driver/data_type_controller.h

Index: components/sync/driver/data_type_controller.h
diff --git a/components/sync/driver/data_type_controller.h b/components/sync/driver/data_type_controller.h
index 1973b84728d929da1300dab6a61ecca3ed04691c..aef685cdbc2cb6afcf85026f484a8db39d22830a 100644
--- a/components/sync/driver/data_type_controller.h
+++ b/components/sync/driver/data_type_controller.h
@@ -159,9 +159,6 @@ class DataTypeController : public base::SupportsWeakPtr<DataTypeController> {
  protected:
   DataTypeController(ModelType type, const base::Closure& dump_stack);
 
-  // Create an error handler that reports back to this controller.
-  virtual std::unique_ptr<DataTypeErrorHandler> CreateErrorHandler() = 0;
-
   // Allows subclasses to DCHECK that they're on the correct thread.
   bool CalledOnValidThread() const;