handleNewPolygon(opt_overlay) {
    this.currentPolygon = opt_overlay;
    $('.region').addClass('selected');
    $('.export').attr('disabled', false);
    this.setDrawingModeEnabled(false);
  }
Stores the current polygon drawn on the map and disables drawing.
@param {Object} opt_overlay The new polygon drawn on the map. If
    undefined, the default polygon is treated as the new polygon.