Fix http://dartbug.com/8669 by making sure we do not crash when trying to use Object as a mixin.

tests/language/mixin_illegal_object_test.dart

 // Copyright (c) 2013, 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 deferred loading requires same library names.
+class C0 extends Object
+with Object                       /// 01: compile-time error
+{ }
 
-import 'dart:async';
-
-@lazy  /// 01: compile-time error
-import 'deferred_function_library.dart';
-
-const lazy = const DeferredLibrary('fisk');
+typedef C1 = Object with Object;  /// 02: compile-time error
 
 main() {
+  new C0();
+  new C1();                       /// 02: continued
 }