static setDisplay(element, display) {
    if (!element) {
      return;
    }

    if (display) {
      // Removing a non-existent class doesn't throw, so, even if
      // the element is not hidden, this should be fine.
      element.classList.remove('shaka-hidden');
    } else {
      element.classList.add('shaka-hidden');
    }
  }
Depending on the value of display, sets/removes the css class of element to
either display it or hide it.

@param {Element} element
@param {boolean} display