anchor.diff:            ),
             new ListItem(
               onTap: () => _handleOptIn(!config.ga.optIn),
  -            left: new Checkbox(
  +            leading: new Checkbox(
                 value: config.ga.optIn,
                 onChanged: _handleOptIn
               ),
  -            primary: new Text("Opt in to analytics")
  +            title: new Text("Opt in to analytics")
             )
           ],
  -        justifyContent: FlexJustifyContent.spaceAround
  +        mainAxisAlignment: MainAxisAlignment.spaceAround
         ),
         floatingActionButton: new FloatingActionButton(
           child: new Icon(icon: Icons.add),
  
positive.code: 
    Widget build(BuildContext context) {
      return new Scaffold(
        toolBar: new ToolBar(
          center: new Text('Usage Example')
        ),
        body: new Column(
          children: <Widget>[
  
negative.code:   runApp(new MaterialApp(
      title: 'Usage Example',
      theme: new ThemeData.dark(),
      routes: <String, WidgetBuilder>{
        '/': (BuildContext context) => new FlutterDemo(ga)
      }
    ));
  }
  
  class FlutterDemo extends StatefulWidget {
    FlutterDemo(this.ga);
    Analytics ga;
    State createState() => new _FlutterDemoState();
  