code: def ref_for_message_type(self, message_type):
      
      name = self.__normalized_name(message_type)
      if name not in self.__schemas:
        raise KeyError('Message has not been parsed: %s', name)
      return name
docs: Returns the JSON Schema id for the given message.
  
      Args:
        message_type: protorpc.message.Message class to be parsed.
  
      Returns:
        string, The JSON Schema id.
  
      Raises:
        KeyError: if the message hasn't been parsed via add_message().