addMessage method

Implementation

@override
void addMessage(MessageModel message) {
  // fix Bad state: Cannot add new events after calling close
  if (messageStreamController.isClosed) return;
  inflateMessage(message);
  // List反转后列是从底部向上展示，所以新来的消息需要插入到数据的第0个位置
  initialMessageList.insert(0, message);
  messageStreamController.sink.add(initialMessageList);
  scrollToLastMessage();
}