code: function(size) {
          var tileSize = (size) ? size :
                                  ((this.tileSize) ? this.tileSize :
                                                     this.map.getTileSize());
          this.tileSize = tileSize;
          if(this.gutter) {
            // layers with gutters need non-null tile sizes
            //if(tileSize == null) {
            //    OpenLayers.console.error("Error in layer.setMap() for " +
            //                              this.name + ": layers with " +
            //                              "gutters need non-null tile sizes");
            //}
              this.imageSize = new OpenLayers.Size(tileSize.w + (2*this.gutter), 
                                                   tileSize.h + (2*this.gutter)); 
          }
      }
docs: APIMethod: setTileSize
  Set the tile size based on the map size.  This also sets layer.imageSize
  or use by Tile.Image.
  
  Parameters:
  size - {<OpenLayers.Size>}