restoreScrollPosition() {

		const scrollPosition = sessionStorage.getItem( 'reveal-scroll-top' );
		const scrollOrigin = sessionStorage.getItem( 'reveal-scroll-origin' );

		if( scrollPosition && scrollOrigin === location.origin + location.pathname ) {
			this.viewportElement.scrollTop = parseInt( scrollPosition, 10 );
		}

	}
Restores the scroll position when a deck is reloader.