Migrated test block 25 to Dart 2.0.

tests/corelib_2/set_intersection_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();
 }
 
@@ skipping 11 matching lines @@
   var setOther = new Set<A>();
   setOther.add(new A());
   var sets = [set1, set2, set3];
   for (var setToTest in sets) {
     // Test that the set accepts another set that is not of the same type:
     //   Set<B>.intersection(Set<A>)
     Set result = setToTest.intersection(setOther);
     Expect.isTrue(result.isEmpty);
   }
 }