_drawDebugInfo( tiledImage, lastDrawn ) {
        if( tiledImage.debugMode ) {
            for ( var i = lastDrawn.length - 1; i >= 0; i-- ) {
                var tile = lastDrawn[ i ];
                try {
                    this._drawDebugInfoOnTile(tile, lastDrawn.length, i, tiledImage);
                } catch(e) {
                    $.console.error(e);
                }
            }
        }
    }
Draws special debug information for a TiledImage if in debug mode.
@private
@param {OpenSeadragon.Tile[]} lastDrawn - An unordered list of Tiles drawn last frame.