'Requests `limit` previous PDUs in a given context before list of
PDUs.
Args:
dest (str)
room_id (str)
event_tuples (list)
limt (int)
Returns:
Deferred: Results in a dict received from the remote homeserver.'

@log_function
def backfill(self, destination, room_id, event_tuples, limit):

    logger.debug('backfill    dest=%s,    room_id=%s,    event_tuples=%s,    limit=%s', destination, room_id, repr(event_tuples), str(limit))
    if (not event_tuples):
        return
    path = (PREFIX + ('/backfill/%s/' % (room_id,)))
    args = {'v': event_tuples, 'limit': [str(limit)]}
    return self.client.get_json(destination, path=path, args=args)
