anchor.diff:  
   /// Host machine running the tests.
   class HostAgent {
  -  HostAgent({@required Platform platform, @required FileSystem fileSystem})
  +  HostAgent({required Platform platform, required FileSystem fileSystem})
         : _platform = platform,
           _fileSystem = fileSystem;
   
  
positive.code: // Copyright 2014 The Flutter 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 = 2.8
  
  import 'package:file/file.dart';
  import 'package:file/local.dart';
  
negative.code:   final FileSystem _fileSystem;
  
    /// Creates a directory to dump file artifacts.
    Directory? get dumpDirectory {
      if (_dumpDirectory == null) {
        // Set in LUCI recipe.
        final String? directoryPath = _platform.environment['FLUTTER_LOGS_DIR'];
        if (directoryPath != null) {
          _dumpDirectory = _fileSystem.directory(directoryPath)..createSync(recursive: true);
          print('Found FLUTTER_LOGS_DIR dump directory ${_dumpDirectory?.path}');
        }
      }
      return _dumpDirectory;
    }
  
    static Directory? _dumpDirectory;
  
    @visibleForTesting
    void resetDumpDirectory() {
  