maps sample - add second fab

main.dart

Align(
 alignment: Alignment.topRight,
 child: Column(
   children: <Widget>[
     FloatingActionButton(
       ...
     ),
     SizedBox(height: 16.0),
     FloatingActionButton(
       onPressed: _onAddMarkerButtonPressed,
       materialTapTargetSize: MaterialTapTargetSize.padded,
       backgroundColor: Colors.green,
       child: const Icon(Icons.add_location, size: 36.0),
     ),
   ],
 ),
),