Migrated test block 25 to Dart 2.0.

tests/corelib_2/set_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.
 
 library set_test;
 
 import 'package:expect/expect.dart';
 import "dart:collection";
 
 void testMain(Set create()) {
@@ skipping 147 matching lines @@
   }
 
   // Test Set.difference.
   Set difference = twice.difference(thrice);
   Expect.equals(5, difference.length);
   for (int i = 0; i < 16; i++) {
     Expect.equals(i.isEven && (i % 3) != 0, difference.contains(i));
   }
   Expect.isTrue(twice.difference(thrice).difference(twice).isEmpty);
 
+  // Test Set.difference with non-element type.
+  Set diffSet = create()..addAll([0, 1, 2, 499, 999]);
+  Set<Object> objectSet = new Set<Object>();
+  objectSet.add("foo");
+  objectSet.add(499);
+  Set diffResult = diffSet.difference(objectSet);
+  Expect.equals(4, diffResult.length);
+  for (int value in [0, 1, 2, 999]) {
+    Expect.isTrue(diffResult.contains(value));
+  }
+
   // Test Set.addAll.
   List list = new List(10);
   for (int i = 0; i < 10; i++) {
     list[i] = i + 10;
   }
   set.addAll(list);
   testLength(20, set);
   for (int i = 0; i < 20; i++) {
     Expect.isTrue(set.contains(i));
   }
@@ skipping 358 matching lines @@
 
   testCESetFrom(
       (x) => new SplayTreeSet<CE>.from(x, customCompare(20), validKey));
   testCESetFrom((x) => new SplayTreeSet<CE>.from(x, identityCompare));
 
   testASetFrom((x) => new Set<A>.from(x));
   testASetFrom((x) => new HashSet<A>.from(x));
   testASetFrom((x) => new LinkedHashSet<A>.from(x));
   testASetFrom((x) => new SplayTreeSet<A>.from(x, identityCompare));
 }