anchor.diff:            Tooltip(
               key: activeFilterKey,
               message: 'Only uncompleted todos',
  +            // ignore: deprecated_member_use, TextButton is not available in stable yet
               child: FlatButton(
                 onPressed: () => filter.state = TodoListFilter.active,
                 visualDensity: VisualDensity.compact,
  
positive.code:           Tooltip(
              key: completedFilterKey,
              message: 'Only completed todos',
              child: FlatButton(
                onPressed: () => filter.state = TodoListFilter.completed,
                visualDensity: VisualDensity.compact,
  
negative.code:           Tooltip(
              key: allFilterKey,
              message: 'All todos',
              // ignore: deprecated_member_use, TextButton is not available in stable yet
              child: FlatButton(
                onPressed: () => filter.state = TodoListFilter.all,
                visualDensity: VisualDensity.compact,
  