message: Also define __reduce_ex__ on _ListWrapper
  May fix an existing unit test in Python 3.7
diff: @@ -418,6 +418,10 @@ class _ListWrapper(List, collections.MutableSequence,
  return copied
  # pylint: enable=protected-access
  + def __reduce_ex__(self, protocol):
  + return (self.__class__,
  + (self._storage,))
  +
  def _make_storage(self, wrapped_list):
  """Use the user's original list for storage."""
  return wrapped_list
  