anchor.diff:    final List<String> _candidates;
   
     /// The time of last modification of the file under [_validPath].
  -  int? _lastModified;
  +  _TimestampAndLength? _lastModified;
   
     /// The resource provider used for polling the files.
     final ResourceProvider _provider;
  
positive.code: 
    /// Returns the modified time of the path or `null` if the file does not
    /// exist.
    int? _pollOne(String path) {
      try {
        var file = _provider.getFile(path);
        return file.modificationStamp;
      } on FileSystemException catch (_) {
        // File doesn't exist, so return null.
        return null;
  
negative.code: 
  class FileInfo {
    String path;
    _TimestampAndLength modified;
    FileInfo(this.path, this.modified);
  }
  
  