Restore old supermixin functionality to shared language tests.

tests/language/mixin_super_bound2_test.dart

 // Copyright (c) 2015, 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.
+// SharedOptions=--supermixin
 
 import "package:expect/expect.dart";
 
 bool inCheckedMode() {
   try {
     var i = 42;
     String s = i;
   } on TypeError catch (e) {
     return true;
   }
@@ skipping 52 matching lines @@
     // type argument List<List<num>> is not a subtype of List<List<int>>.
     Expect.throws(() => new MNA4<int, num, bool>(), (e) => e is TypeError);
   } else {
     new MNA<int, num, bool>();
     new MNA2<int, num, bool>();
     new MNA3<int, num, bool>();
     new MNA4<int, num, bool>();
   }
 }