Add visit_overloaded() to TypeTranslator.

Part of #730.

Author: JamesGuthrie

mypy/types.py

@@ -631,6 +631,10 @@ def translate_variables(self,
                             variables: List[TypeVarDef]) -> List[TypeVarDef]:
         return variables
 
+    def visit_overloaded(self, type: Overloaded) -> Type:
+        items = [t.accept(self) for t in type.items()]  # type: ignore
+        return Overloaded(items=cast(List[CallableType], items))
+
 
 class TypeStrVisitor(TypeVisitor[str]):
     """Visitor for pretty-printing types into strings.