Add SameTypeVisitor.visit_overloaded() implementation

part of #730

Author: JamesGuthrie

mypy/sametypes.py

@@ -2,7 +2,7 @@
 
 from mypy.types import (
     Type, UnboundType, ErrorType, AnyType, NoneTyp, Void, TupleType, UnionType, CallableType,
-    TypeVarType, Instance, TypeVisitor, ErasedType, TypeList
+    TypeVarType, Instance, TypeVisitor, ErasedType, TypeList, Overloaded
 )
 
 
@@ -91,3 +91,10 @@ def visit_union_type(self, left: UnionType) -> bool:
             return is_same_types(left.items, cast(UnionType, self.right).items)
         else:
             return False
+
+    def visit_overloaded(self, left: Overloaded) -> bool:
+        if isinstance(self.right, Overloaded):
+            return is_same_types(cast(List[Type], left.items()),
+                                 cast(List[Type], cast(Overloaded, self.right).items()))
+        else:
+            return False