anchor.diff:  // Copyright 2020 The Chromium Authors. All rights reserved.
   // Use of this source code is governed by a BSD-style license that can be
   // found in the LICENSE file.
  -
  -// @dart=2.9
   
   import 'dart:async';
   
  
positive.code: class _ExampleConditionalScreenBodyState
      extends State<_ExampleConditionalScreenBody>
      with OfflineScreenMixin<_ExampleConditionalScreenBody, String> {
    ExampleController controller;
  
    @override
    void didChangeDependencies() {
  
negative.code: 
    @override
    Widget build(BuildContext context) {
      final exampleScreen = ValueListenableBuilder<String>(
        valueListenable: controller!.title,
        builder: (context, String value, _) {
          return Center(child: Text(value));
        },
      );
  