anchor.diff:      Source definingSource,
       CompilationUnit definingUnit,
       List<LinkInputUnit> units,
  +    FeatureSet featureSet,
     ) {
       units.add(
         LinkInputUnit(null, definingSource, false, definingUnit),
  
positive.code:     var unit = parseText(text, featureSet);
  
      var units = <LinkInputUnit>[];
      _addLibraryUnits(source, unit, units);
      libraries.add(
        LinkInputLibrary(source, units),
      );
  
negative.code:       var unit = parseText(text, featureSet);
  
        var inputUnits = <LinkInputUnit>[];
        _addLibraryUnits(source, unit, inputUnits, featureSet);
        inputLibraries.add(
          LinkInputLibrary(source, inputUnits),
        );
  