function showBackdrop(scope, element, options) {
      if (options.nestLevel) return angular.noop;

      // If we are not within a dialog...
      if (options.disableParentScroll && !$mdUtil.getClosest(options.target, 'MD-DIALOG')) {
        // !! DO this before creating the backdrop; since disableScrollAround()
        //    configures the scroll offset; which is used by mdBackDrop postLink()
        options.restoreScroll = $mdUtil.disableScrollAround(options.element, options.parent);
      } else {
        options.disableParentScroll = false;
      }

      if (options.hasBackdrop) {
        options.backdrop = $mdUtil.createBackdrop(scope, "md-menu-backdrop md-click-catcher");

        $animate.enter(options.backdrop, options.backdropParent || $document[0].body);
      }

      /**
       * Hide and destroys the backdrop created by showBackdrop()
       */
      return function hideBackdrop() {
        if (options.backdrop) options.backdrop.remove();
        if (options.disableParentScroll) options.restoreScroll();
      };
    }
Show modal backdrop element...
@returns {function(): void} A function that removes this backdrop