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