testActiveElementAlreadyFocused() {
    const element = document.getElementById('textInput');
    element.style.display = '';
    element.focus();

    assertNull(mh.activeElement_);

    mh.attachInput(element);
    assertEquals(element, mh.activeElement_);

    mh.detachInput(element);
    element.style.display = 'none';
  }
Make sure an already-focused element becomes active immediately.
     @suppress {visibility} suppression added to enable type checking