anchor.diff:        ..remove(canonicalFile)
         ..insert(0, canonicalFile);
     }
  +
  +  void _addFileWithPath(String path, FileState file) {
  +    var files = _pathToFiles[path];
  +    if (files == null) {
  +      knownFilePaths.add(path);
  +      files = <FileState>[];
  +      _pathToFiles[path] = files;
  +    }
  +    files.add(file);
  +  }
   }
   
   @visibleForTesting
  
positive.code:       this._sdkApiSignature) {
      _testView = new FileSystemStateTestView(this);
    }
  
    /**
     * Return the set of known file paths.
     */
    Set<String> get knownFilePaths => _pathToFiles.keys.toSet();
  
    /**
     * Return the known files.
  
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 = {};
  