code: function () {
  
              var nViewportOffset = Overlay.VIEWPORT_OFFSET,
                  elementWidth = this.element.offsetWidth,
                  elementHeight = this.element.offsetHeight,
                  viewPortWidth = Dom.getViewportWidth(),
                  viewPortHeight = Dom.getViewportHeight(),
                  x,
                  y;
  
              if (elementWidth < viewPortWidth) {
                  x = (viewPortWidth / 2) - (elementWidth / 2) + Dom.getDocumentScrollLeft();
              } else {
                  x = nViewportOffset + Dom.getDocumentScrollLeft();
              }
  
              if (elementHeight < viewPortHeight) {
                  y = (viewPortHeight / 2) - (elementHeight / 2) + Dom.getDocumentScrollTop();
              } else {
                  y = nViewportOffset + Dom.getDocumentScrollTop();
              }
  
              this.cfg.setProperty("xy", [parseInt(x, 10), parseInt(y, 10)]);
              this.cfg.refireEvent("iframe");
  
              if (UA.webkit) {
                  this.forceContainerRedraw();
              }
          }
docs: Centers the container in the viewport.
  @method center