anchor.diff:      url '$urlBase/stable/release/${revisions['stable']}/$ia32File'
       sha256 '${hashes['stable'][ia32File]}'
     end
  +
  +  option 'with-content-shell', 'Download and install content_shell -- headless Dartium for testing'
  +  option 'with-dartium', 'Download and install Dartium -- Chromium with Dart'
   
     devel do
       version '$devVersion'
  
positive.code: 
      resource 'content_shell' do
        url '$urlBase/dev/release/${revisions['dev']}/$contentShellFile'
        version '$devVersion'
        sha256 '${hashes['dev'][contentShellFile]}'
      end
    end
  
    resource 'content_shell' do
      url '$urlBase/stable/release/${revisions['stable']}/$contentShellFile'
      version '$stableVersion'
      sha256 '${hashes['stable'][contentShellFile]}'
    end
  
  
negative.code:   final options = parser.parse(args);
    final revision = options['revision'];
    final channel = options['channel'];
    if ([revision, channel].contains(null)) {
      print("Usage: update_homebrew.dart -r revision -c channel [-k ssh_key]\n"
          "  ssh_key should allow pushes to ${GITHUB_REPO} on github");
      return;
    }
  
    final key = options['key'];
    if (key != null) {
      final sshWrapper = Platform.script.resolve('ssh_with_key').toFilePath();
      gitEnvironment = {'GIT_SSH': sshWrapper, 'SSH_KEY_PATH': key};
    }
  
    Chain.capture(() async {
      var tempDir = await Directory.systemTemp.createTemp('update_homebrew');
  