Fix memoryview stub (#651)

Fixes python/mypy#2390

stdlib/3/builtins.pyi

@@ -1,7 +1,7 @@
 # Stubs for builtins (Python 3)
 
 from typing import (
-    TypeVar, Iterator, Iterable, overload,
+    TypeVar, Iterator, Iterable, overload, Container,
     Sequence, MutableSequence, Mapping, MutableMapping, Tuple, List, Any, Dict, Callable, Generic,
     Set, AbstractSet, MutableSet, Sized, Reversible, SupportsInt, SupportsFloat, SupportsBytes,
     SupportsAbs, SupportsRound, IO, Union, ItemsView, KeysView, ValuesView, ByteString, Optional
@@ -422,12 +422,41 @@ class bytearray(MutableSequence[int], ByteString):
     def __gt__(self, x: bytes) -> bool: ...
     def __ge__(self, x: bytes) -> bool: ...
 
-class memoryview():
-    # TODO arg can be any obj supporting the buffer protocol
-    def __init__(self, b: bytearray) -> None: ...
+
+class memoryview(Sized, Container[bytes]):
+    format = ... # type: str
+    itemsize = ... # type: int
+    shape = ... # type: Optional[Tuple[int, ...]]
+    strides = ... # type: Optional[Tuple[int, ...]]
+    suboffsets = ... # type: Optional[Tuple[int, ...]]
+    readonly = ... # type: bool
+    ndim = ... # type: int
+
+    def __init__(self, obj: Union[str, bytes, bytearray, memoryview]) -> None: ...
+
+    @overload
+    def __getitem__(self, i: int) -> int: ...
+    @overload
+    def __getitem__(self, s: slice) -> memoryview: ...
+
+    def __contains__(self, x: object) -> bool: ...
+    def __iter__(self) -> Iterator[bytes]: ...
+    def __len__(self) -> int: ...
+
+    @overload
+    def __setitem__(self, i: int, o: bytes) -> None: ...
+    @overload
+    def __setitem__(self, s: slice, o: Sequence[bytes]) -> None: ...
+    @overload
+    def __setitem__(self, s: slice, o: memoryview) -> None: ...
+
+    def tobytes(self) -> bytes: ...
+    def tolist(self) -> List[int]: ...
+
     if sys.version_info >= (3, 5):
         def hex(self) -> str: ...
 
+
 class bool(int, SupportsInt, SupportsFloat):
     def __init__(self, o: object = ...) -> None: ...
 
@@ -694,7 +723,6 @@ def map(func: Callable[[_T1, _T2], _S], iter1: Iterable[_T1],
 def max(arg1: _T, arg2: _T, *args: _T, key: Callable[[_T], Any] = ...) -> _T: ...
 @overload
 def max(iterable: Iterable[_T], key: Callable[[_T], Any] = ..., default:_T = ...) -> _T: ...
-# TODO memoryview
 @overload
 def min(arg1: _T, arg2: _T, *args: _T, key: Callable[[_T], Any] = ...) -> _T: ...
 @overload