function updateIsLocked(isLocked, oldValue) {
      scope.isLockedOpen = isLocked;
      if (isLocked === oldValue) {
        element.toggleClass('md-locked-open', !!isLocked);
      } else {
        $animate[isLocked ? 'addClass' : 'removeClass'](element, 'md-locked-open');
      }
      if (backdrop) {
        backdrop.toggleClass('md-locked-open', !!isLocked);
      }
    }
Toggle the DOM classes to indicate `locked`
@param isLocked
@param oldValue