Migrated test block 16 to Dart 2.0.

tests/corelib_strong/map_keys_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";
-
-main() {
-  var map1 = {"foo": 42, "bar": 499};
-  var map2 = {};
-  var map3 = const {"foo": 42, "bar": 499};
-  var map4 = const {};
-  var map5 = new Map<String, int>();
-  map5["foo"] = 43;
-  map5["bar"] = 500;
-  var map6 = new Map<String, bool>();
-
-  Expect.isTrue(map1.keys is Iterable);
-  Expect.isFalse(map1.keys is List);
-  Expect.equals(2, map1.keys.length);
-  Expect.equals("foo", map1.keys.first);
-  Expect.equals("bar", map1.keys.last);
-
-  Expect.isTrue(map2.keys is Iterable);
-  Expect.isFalse(map2.keys is List);
-  Expect.equals(0, map2.keys.length);
-
-  Expect.isTrue(map3.keys is Iterable);
-  Expect.isFalse(map3.keys is List);
-  Expect.equals(2, map3.keys.length);
-  Expect.equals("foo", map3.keys.first);
-  Expect.equals("bar", map3.keys.last);
-
-  Expect.isTrue(map4.keys is Iterable);
-  Expect.isFalse(map4.keys is List);
-  Expect.equals(0, map4.keys.length);
-
-  Expect.isTrue(map5.keys is Iterable);
-  Expect.isFalse(map5.keys is List);
-  Expect.equals(2, map5.keys.length);
-  Expect.isTrue(map5.keys.first == "foo" || map5.keys.first == "bar");
-  Expect.isTrue(map5.keys.last == "foo" || map5.keys.last == "bar");
-  Expect.notEquals(map5.keys.first, map5.keys.last);
-
-  Expect.isTrue(map6.keys is Iterable);
-  Expect.isFalse(map6.keys is List);
-  Expect.equals(0, map6.keys.length);
-}