Grants approval for a given request.

def _GrantApproval(self, requestor_username, approval_id, grantor_username,
                     cursor):
    """Grants approval for a given request."""
    grant_args = {
        "username_hash": mysql_utils.Hash(requestor_username),
        "approval_id": approval_id,
        "grantor_username_hash": mysql_utils.Hash(grantor_username),
    }
    grant_query = (
        "INSERT INTO approval_grant {columns} VALUES {values}".format(
            columns=mysql_utils.Columns(grant_args),
            values=mysql_utils.NamedPlaceholders(grant_args)))
    cursor.execute(grant_query, grant_args)