getPolygonCoordinates() {
    var points = this.currentPolygon.getPath().getArray();
    var twoDimensionalArray = points.map(function(point) {
      return [point.lng(), point.lat()];
    });
    return twoDimensionalArray;
  }
Returns the coordinates of the currently drawn polygon.
@return {Array<Array<number>>} A list of coordinates describing
    the currently drawn polygon (or null if no polygon is drawn).