docs: public WebSocket flush()
      {
          synchronized (mStateManager)
          {
              WebSocketState state = mStateManager.getState();
  
              if (state != OPEN && state != CLOSING)
              {
                  return this;
              }
          }
  
          // Get the reference to the instance of WritingThread.
          WritingThread wt = mWritingThread;
  
          // If and only if an instance of WritingThread is available.
          if (wt != null)
          {
              // Request flush.
              wt.queueFlush();
          }
  
          return this;
      }