Migrated test block 25 to Dart 2.0.

tests/corelib/set_containsAll_test.dart

-// Copyright (c) 2011, 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 "package:expect/expect.dart";
-
-class A {
-  const A();
-}
-
-class B extends A {
-  const B();
-}
-
-main() {
-  var set1 = new Set<B>();
-  set1.add(const B());
-  var set2 = new Set<B>();
-  var list = <B>[const B()];
-  var set3 = list.toSet();
-
-  var sets = [set1, set2, set3];
-  for (var setToTest in sets) {
-    Expect.isFalse(setToTest.containsAll(<A>[new A()]));
-  }
-}