Migrate test block 10 to Dart 2.0.

tests/corelib_strong/iterable_contains2_test.dart

-// Copyright (c) 2012, 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";
-
-// Tests for the contains methods on lists.
-
-class A {
-  const A();
-}
-
-class B extends A {
-  const B();
-}
-
-main() {
-  var list = <B>[new B()];
-  var set = new Set<B>();
-  set.add(new B());
-  var iterable1 = list.map((x) => x);
-  var iterable2 = list.take(1);
-  var list2 = const <B>[const B()];
-  var iterable3 = list2.map((x) => x);
-  var iterable4 = list2.take(1);
-  var iterables = [
-    list,
-    set,
-    iterable1,
-    iterable2,
-    list2,
-    iterable3,
-    iterable4
-  ];
-  for (var iterable in iterables) {
-    Expect.isFalse(iterable.contains(new A()));
-  }
-}