anchor.diff:  }
   
   
  +_extractDriveLetterPrefix(cwd) {
  +  if (!_isWindows) {
  +    return null;
  +  }
  +  if (cwd.length > 1 && cwd[1] == ':') {
  +    return '/${cwd[0]}:';
  +  }
  +  return null;
  +}
  +
  +
   void _setWorkingDirectory(cwd) {
  +  _workingWindowsDrivePrefix = _extractDriveLetterPrefix(cwd);
     cwd = _sanitizeWindowsPath(cwd);
     cwd = _enforceTrailingSlash(cwd);
     _workingDirectoryUri = new Uri(scheme: 'file', path: cwd);
  
positive.code:   return fixedPath;
  }
  
  _enforceTrailingSlash(uri) {
    // Ensure we have a trailing slash character.
    if (!uri.endsWith('/')) {
  
negative.code:     throw "URIs using the 'file:' scheme may not contain a host.";
    }
  
    String path = uri.path;
    _logResolution('# Path: $uri -> ${path}');
    // Check that the path is not already in the form of /X:.
    if (_isWindows && (path.length > 2) && path.startsWith('/') &&
        (path[2] != ':')) {
      // Absolute path on Windows without a drive letter.
      if (_workingWindowsDrivePrefix == null) {
        throw 'Could not determine windows drive letter prefix.';
      }
      _logResolution('# Path: Windows absolute path needs a drive letter.'
                     ' Prepending $_workingWindowsDrivePrefix.');
      path = '$_workingWindowsDrivePrefix$path';
    }
    return path;
  }
  
  
  