Add a "change" to delete a document.

        See
        :meth:`~.firestore_v1beta1.document.DocumentReference.delete` for
        more information on how ``option`` determines how the change is
        applied.

        Args:
            reference (~.firestore_v1beta1.document.DocumentReference): A
               document reference that will be deleted in this batch.
            option (Optional[~.firestore_v1beta1.client.WriteOption]): A
               write option to make assertions / preconditions on the server
               state of the document before applying changes.

def delete(self, reference, option=None):
        """Add a "change" to delete a document.

        See
        :meth:`~.firestore_v1beta1.document.DocumentReference.delete` for
        more information on how ``option`` determines how the change is
        applied.

        Args:
            reference (~.firestore_v1beta1.document.DocumentReference): A
               document reference that will be deleted in this batch.
            option (Optional[~.firestore_v1beta1.client.WriteOption]): A
               write option to make assertions / preconditions on the server
               state of the document before applying changes.
        """
        write_pb = _helpers.pb_for_delete(reference._document_path, option)
        self._add_write_pbs([write_pb])