code: 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);
        }
      }
docs: Toggle the DOM classes to indicate `locked`
  @param isLocked
  @param oldValue