code: function() {
          var backBuffer;
          if(this.useIFrame === false) {
              backBuffer = OpenLayers.Tile.Image.prototype.createBackBuffer.call(this);
          }
          return backBuffer;
      }
docs: Method: createBackBuffer
  Override createBackBuffer to do nothing when we use an iframe. Moving an
  iframe from one element to another makes it necessary to reload the iframe
  because its content is lost. So we just give up.
  
  Returns:
  {DOMElement}