Maps Sample V2 - add onAddmarkerButtonPressed() pt 3 - implement method

main.dart

void _onAddMarkerButtonPressed() {
  setState(() {
    _markers.add(Marker(
      // This marker id can be anything that uniquely identifies each marker.
      markerId: MarkerId(_lastMapPosition.toString()),
      position: _lastMapPosition,
      infoWindow: InfoWindow(
        title: 'Really cool place',
        snippet: '5 Star Rating',
      ),
      icon: BitmapDescriptor.defaultMarker,
    ));
  });
}