constructor(mapType, polygonIds) {
    // Create and display the map.
    this.map = this.createMap(mapType);

    // Add the polygons to the map.
    this.addPolygons(polygonIds);

    // Register a click handler to show a panel when the user clicks on a place.
    this.map.data.addListener('click', this.handlePolygonClick.bind(this));

    // Register a click handler to hide the panel when the user clicks close.
    $('.panel .close').click(this.hidePanel.bind(this));

    // Register a click handler to expand the panel when the user taps on
    // toggle.
    $('.panel .toggler').click((function() {
                                 $('.panel').toggleClass('expanded');
                               }).bind(this));
  }
@param {google.maps.ImageMapType} mapType The map type to render on the
    map.
@param {Array<string>} polygonIds The IDs of the polygons to show on the
    map. For example ['poland', 'moldova'].