testPositionMenu() {
    const node = dom.getElement('demoMenuButton');
    menuButton.decorate(node);
    const menu = menuButton.getMenu();
    menu.setVisible(true, true);

    // Move to 500, 500
    menu.setPosition(500, 500);

    // Now reposition and make sure position is more or less ok.
    menuButton.positionMenu();
    const menuNode = dom.getElement('demoMenu');
    assertRoughlyEquals(
        menuNode.offsetTop, node.offsetTop + node.offsetHeight, 20);
    assertRoughlyEquals(menuNode.offsetLeft, node.offsetLeft, 20);
  }
Renders the menu button, moves its menu and then repositions to make sure
the position is more or less ok.
@suppress {strictMissingProperties} suppression added to enable type
checking