anchor.diff:    /// [skipCheck] does not attempt to make a devtools connection before returning.
     Future<Chromium> launch(String url, {
       bool headless = false,
  -    int debugPort,
  +    int? debugPort,
       bool skipCheck = false,
  -    Directory cacheDir,
  +    Directory? cacheDir,
     }) async {
       if (currentCompleter.isCompleted) {
         throwToolExit('Only one instance of chrome can be started.');
  
positive.code:   if (platform.isWindows) {
      /// The possible locations where the chrome executable can be located on windows.
      final List<String> kWindowsPrefixes = <String>[
        platform.environment['LOCALAPPDATA'],
        platform.environment['PROGRAMFILES'],
        platform.environment['PROGRAMFILES(X86)'],
      ];
      final String windowsPrefix = kWindowsPrefixes.firstWhere((String prefix) {
        if (prefix == null) {
  
negative.code:   /// Restore Chrome user information from a per-project cache into Chrome's
    /// user data directory.
    void _restoreUserSessionInformation(Directory cacheDir, Directory userDataDir) {
      final Directory sourceChromeDefault = _fileSystem.directory(_fileSystem.path.join(cacheDir.path, _chromeDefaultPath));
      final Directory targetChromeDefault = _fileSystem.directory(_fileSystem.path.join(userDataDir.path, _chromeDefaultPath));
      try {
        if (sourceChromeDefault.existsSync()) {
  