code: function(contentSize) { 
          OpenLayers.Popup.prototype.setSize.apply(this, arguments);
  
          if ((this.lonlat) && (this.map)) {
              var px = this.map.getLayerPxFromLonLat(this.lonlat);
              this.moveTo(px);
          }
      }
docs: APIMethod: setSize
  
  Parameters:
  contentSize - {<OpenLayers.Size>} the new size for the popup's
  contents div (in pixels).