restoreScroll = function() {
                $.setPageScroll( _this.pageScroll );
                var pageScroll = $.getPageScroll();
                restoreScrollCounter++;
                if (restoreScrollCounter < 10 &&
                    (pageScroll.x !== _this.pageScroll.x ||
                    pageScroll.y !== _this.pageScroll.y)) {
                    $.requestAnimationFrame( restoreScroll );
                }
            }
Raised when the viewer is about to change to/from full-page mode (see {@link OpenSeadragon.Viewer#setFullPage}).

@event pre-full-page
@memberof OpenSeadragon.Viewer
@type {object}
@property {OpenSeadragon.Viewer} eventSource - A reference to the Viewer which raised the event.
@property {Boolean} fullPage - True if entering full-page mode, false if exiting full-page mode.
@property {Boolean} preventDefaultAction - Set to true to prevent full-page mode change. Default: false.
@property {?Object} userData - Arbitrary subscriber-defined object.