anchor.diff:  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';
  
positive.code:         return;
        }
  
        js.Node receiver = node.receiver;
        String receiverName;
        if (receiver is js.VariableUse) {
          receiverName = receiver.name;
  
negative.code:         receiverName = 'this';
        }
  
        js.Node selector = undefer(node.selector);
        String name;
        if (selector is js.Name) {
          name = selector.key;
  