Reapply dart2js: Dot-separated field-and-super descriptor string in classes.

tests/compiler/dart2js/no_constructor_body_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.
 
 import 'compiler_helper.dart';
 
 const String TEST = r"""
 class A {
   A.foo() {}
   A();
 }
 main() {
   new A();
   new A.foo();
 }
 """;
 
 main() {
   String generated = compileAll(TEST);
   Expect.isTrue(
-      generated.contains('\$.A = {\n "super": "Object"\n}'));
+      generated.contains('\$.A = {"":"Object;"\n}'));
 }