anchor.diff:        FileSource uriSource = new FileSource(resource, uri);
         file = new FileState._(this, path, uri, uriSource);
         _uriToFile[uri] = file;
  -      _pathToFiles.putIfAbsent(path, () => <FileState>[]).add(file);
  +      _addFileWithPath(path, file);
         _pathToCanonicalFile[path] = file;
         file.refresh();
       }
  
positive.code:       FileSource source = new FileSource(resource, uri);
        file = new FileState._(this, path, uri, source);
        _uriToFile[uri] = file;
        _pathToFiles.putIfAbsent(path, () => <FileState>[]).add(file);
        file.refresh();
      }
      return file;
  
negative.code:   final Map<Uri, FileState> _uriToFile = {};
  
    /**
     * All known file paths.
     */
    final Set<String> knownFilePaths = new Set<String>();
  
    /**
     * Mapping from a path to the corresponding [FileState]s, canonical or not.
     */
    final Map<String, List<FileState>> _pathToFiles = {};
  