int: Size of the queue.

def queue_size(self):
        """int: Size of the queue."""
        response = self.contentDirectory.Browse([
            ('ObjectID', 'Q:0'),
            ('BrowseFlag', 'BrowseMetadata'),
            ('Filter', '*'),
            ('StartingIndex', 0),
            ('RequestedCount', 1),
            ('SortCriteria', '')
        ])
        dom = XML.fromstring(really_utf8(response['Result']))

        queue_size = None
        container = dom.find(
            '{urn:schemas-upnp-org:metadata-1-0/DIDL-Lite/}container')
        if container is not None:
            child_count = container.get('childCount')
            if child_count is not None:
                queue_size = int(child_count)

        return queue_size