Proto dict must have 'row' and 'col' keys.

def from_proto_dict(proto_dict: Dict) -> 'GridQubit':
        """Proto dict must have 'row' and 'col' keys."""
        if 'row' not in proto_dict or 'col' not in proto_dict:
            raise ValueError(
                'Proto dict does not contain row or col: {}'.format(proto_dict))
        return GridQubit(row=proto_dict['row'], col=proto_dict['col'])