anchor.diff:      if (typeInformation.isNotEmpty) {
         FunctionElement helper = glue.getAddRuntimeTypeInformation();
         js.Expression typeArguments = new js.ArrayInitializer(
  -          typeInformation.map(visitExpression).toList());
  +          visitExpressionList(typeInformation));
         return buildStaticHelperInvocation(helper,
             <js.Expression>[instance, typeArguments]);
       } else {
  
positive.code:   @override
    js.Expression visitTypeOperator(tree_ir.TypeOperator node) {
      js.Expression value = visitExpression(node.value);
      List<js.Expression> typeArguments =
          node.typeArguments.map(visitExpression).toList();
      if (!node.isTypeTest) {
        giveup(node, 'type casts not implemented.');
      }
  
negative.code: 
    @override
    js.Expression visitCreateBox(tree_ir.CreateBox node) {
      return new js.ObjectInitializer(const <js.Property>[]);
    }
  
    @override
  