How to use the @lumino/messaging.MessageLoop.flush function in @lumino/messaging

previousWidget.hide();
    }

    // Show the current widget.
    if (currentWidget) {
      currentWidget.show();
    }

    // Emit the `currentChanged` signal for the tab panel.
    this._currentChanged.emit({
      previousIndex, previousWidget, currentIndex, currentWidget
    });

    // Flush the message loop on IE and Edge to prevent flicker.
    if (Platform.IS_EDGE || Platform.IS_IE) {
      MessageLoop.flush();
    }
  }

// Rehydrate the left area.
    if (leftArea) {
      this._leftHandler.rehydrate(leftArea);
    }

    // Rehydrate the right area.
    if (rightArea) {
      this._rightHandler.rehydrate(rightArea);
    }

    if (!this._isRestored) {
      // Make sure all messages in the queue are finished before notifying
      // any extensions that are waiting for the promise that guarantees the
      // application state has been restored.
      MessageLoop.flush();
      this._restored.resolve(layout);
    }
  }

// Extract the previous and current title from the args.
    let { previousTitle, currentTitle } = args;

    // Hide the previous widget.
    if (previousTitle) {
      previousTitle.owner.hide();
    }

    // Show the current widget.
    if (currentTitle) {
      currentTitle.owner.show();
    }

    // Flush the message loop on IE and Edge to prevent flicker.
    if (Platform.IS_EDGE || Platform.IS_IE) {
      MessageLoop.flush();
    }

    // Schedule an emit of the layout modified signal.
    MessageLoop.postMessage(this, Private.LayoutModified);
  }

restoreLayout(config: DockPanel.ILayoutConfig): void {
    // Reset the mode.
    this._mode = 'multiple-document';

    // Restore the layout.
    (this.layout as DockLayout).restoreLayout(config);

    // Flush the message loop on IE and Edge to prevent flicker.
    if (Platform.IS_EDGE || Platform.IS_IE) {
      MessageLoop.flush();
    }

    // Schedule an emit of the layout modified signal.
    MessageLoop.postMessage(this, Private.LayoutModified);
  }