anchor.diff:    void registerCalls(Features features, String tag, js.Node node,
         {String prefix = '', Set<js.PropertyAccess> handledAccesses}) {
       forEachNode(node, onCall: (js.Call node) {
  -      js.Node target = node.target;
  +      js.Node target = undefer(node.target);
         if (target is js.PropertyAccess) {
  -        js.Node selector = target.selector;
  +        js.Node selector = undefer(target.selector);
           bool fixedNameCall = false;
           String name;
           if (selector is js.Name) {
  
positive.code:         receiverName = 'this';
        }
  
        js.Node selector = node.selector;
        String name;
        if (selector is js.Name) {
          name = selector.key;
  
negative.code: import 'package:async_helper/async_helper.dart';
  import 'package:compiler/src/closure.dart';
  import 'package:compiler/src/common.dart';
  import 'package:compiler/src/common/codegen.dart';
  import 'package:compiler/src/compiler.dart';
  import 'package:compiler/src/diagnostics/diagnostic_listener.dart';
  import 'package:compiler/src/elements/entities.dart';
  