Legacy access to owner role.

        DEPRECATED:  use ``policy["roles/owners"]`` instead.

def owners(self):
        """Legacy access to owner role.

        DEPRECATED:  use ``policy["roles/owners"]`` instead."""
        result = set()
        for role in self._OWNER_ROLES:
            for member in self._bindings.get(role, ()):
                result.add(member)
        return frozenset(result)