static focusOnTheChosenItem(menu) {
    if (!menu) {
      return;
    }
    const chosenItem = shaka.ui.Utils.getDescendantIfExists(
        menu, 'shaka-chosen-item');
    if (chosenItem) {
      chosenItem.parentElement.focus();
    }
  }
Finds a descendant of |menu| that has a 'shaka-chosen-item' class
and focuses on its' parent.

@param {HTMLElement} menu