Add the (deprecated) assertDictContainsSubset() to TestCase. (#3437)

Until this is removed from the standard library, it probably should stay in the typing.

Also update both 2 and 3 definitions to use Mapping[Any, Any], rather than Dict[Any, Any].

stdlib/2/unittest.pyi

@@ -3,8 +3,8 @@
 # Based on http://docs.python.org/2.7/library/unittest.html
 
 from typing import (Any, Callable, Dict, FrozenSet, Iterable, Iterator,
-                    List, NoReturn, Optional, overload, Pattern, Sequence, Set,
-                    Text, TextIO, Tuple, Type, TypeVar, Union)
+                    List, Mapping, NoReturn, Optional, overload, Pattern,
+                    Sequence, Set, Text, TextIO, Tuple, Type, TypeVar, Union)
 from abc import abstractmethod, ABCMeta
 import datetime
 import types
@@ -166,7 +166,10 @@ class TestCase(Testable):
     def assertRegexpMatches(self, text: Text, regexp: _Regexp, msg: object = ...) -> None: ...
     def assertNotRegexpMatches(self, text: Text, regexp: _Regexp, msg: object = ...) -> None: ...
     def assertItemsEqual(self, first: Iterable[Any], second: Iterable[Any], msg: object = ...) -> None: ...
-    def assertDictContainsSubset(self, expected: Dict[Any, Any], actual: Dict[Any, Any], msg: object = ...) -> None: ...
+    def assertDictContainsSubset(self,
+                                 expected: Mapping[Any, Any],
+                                 actual: Mapping[Any, Any],
+                                 msg: object = ...) -> None: ...
     def addTypeEqualityFunc(self, typeobj: type, function: Callable[..., None]) -> None: ...
     @overload
     def failUnlessRaises(self, exception: _ExceptionType, callable: Callable[..., Any], *args: Any, **kwargs: Any) -> None: ...