dart2js: Use js('source') instead of js['source'] to invoke JS mini-parser

tests/compiler/dart2js/class_codegen_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Test that parameters keep their names in the output.
 
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST_ONE = r"""
 class A { }
@@ skipping 46 matching lines @@
   A(a) : this.a = a {}
 }
 
 main() {
   new A(3);
 }
 """;
 
 twoClasses() {
   String generated = compileAll(TEST_ONE);
+  print(generated);
   Expect.isTrue(generated.contains('\$.A = {"": "Object;"'));
   Expect.isTrue(generated.contains('\$.B = {"": "Object;"'));
 }
 
 subClass() {
   checkOutput(String generated) {
     Expect.isTrue(generated.contains('\$.A = {"": "Object;"'));
     Expect.isTrue(generated.contains('\$.B = {"": "A;"'));
   }
 
@@ skipping 10 matching lines @@
   String generated = compileAll(TEST_FIVE);
   Expect.isTrue(generated.contains(r"new $.A(a);"));
 }
 
 main() {
   twoClasses();
   subClass();
   fieldTest();
   constructor1();
 }