docs: def size(self, destination):
          """
          Size of the queue for specified destination.
  
          @param destination: The queue destination (e.g. /queue/foo)
          @type destination: C{str}
  
          @return: The number of frames in specified queue.
          @rtype: C{int}
          """
          if not destination in self.queue_metadata:
              return 0
          else:
              return len(self.queue_metadata[destination]['frames'])