anchor.diff:      Map<FileState, UnitAnalysisResult> results = {};
       units.forEach((file, unit) {
         List<AnalysisError> errors = _getErrorListener(file).errors;
  +      errors = _filterIgnoredErrors(file, errors);
         results[file] = new UnitAnalysisResult(file, unit, errors);
       });
       return results;
  
positive.code:     analysisContext.sourceFactory = _sourceFactory.clone();
      analysisContext.contentCache = new _ContentCacheWrapper(_fsState);
      this._context = analysisContext;
    }
  
    RecordingErrorListener _getErrorListener(FileState file) =>
  
negative.code:   CompilationUnit _parse(FileState file) {
      RecordingErrorListener errorListener = _getErrorListener(file);
  
      String content = file.content;
  
      CharSequenceReader reader = new CharSequenceReader(content);
      Scanner scanner = new Scanner(file.source, reader, errorListener);
      scanner.scanGenericMethodComments = _analysisOptions.strongMode;
      Token token = scanner.tokenize();
      LineInfo lineInfo = new LineInfo(scanner.lineStarts);
  
      _fileToLineInfo[file] = lineInfo;
      _fileToIgnoreInfo[file] = IgnoreInfo.calculateIgnores(content, lineInfo);
  
      Parser parser = new Parser(file.source, errorListener);
      parser.parseGenericMethodComments = _analysisOptions.strongMode;
  