anchor.diff:  import 'universe/universe.dart' as universe;
   import 'util/util.dart' as util;
   
  +import 'scanner/scannerlib.dart' show
  +    PartialClassElement,
  +    PartialFunctionElement;
  +
   class ElementVisitor extends elements_visitor.ElementVisitor {
     visitElement(e) {}
   }
  
positive.code:   sourceFileProvider.readStringFromUri(null);
  }
  
  useElements(elements.ClassElement e, elements.Name n, modelx.FieldElementX f) {
    e.lookupClassMember(null);
    e.lookupInterfaceMember(null);
    n.isAccessibleFrom(null);
    f.reuseElement();
  }
  
  useIr(cps_ir_nodes_sexpr.SExpressionStringifier stringifier,
  
negative.code:   useSsa(null);
    useCodeBuffer(null);
    usedByTests();
    useElements(null, null, null, null, null);
    useIr(null, null, null);
    useCompiler(null);
    useTypes();
  