code: @JsIgnore
    public static void onReady(Runnable callback) {
      if (isReady) {
        callback.run();
        return;
      }
  
      onReadyCallbacks.push(callback);
    }
docs: Ask to be warned when Vue GWT is ready. If Vue GWT is ready, the callback is called
  immediately.
  
  @param callback The callback to call when Vue GWT is ready.