Revert "Remove Expect from core library."

tests/language/ordered_maps_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";
-
 // Tests that map literals are ordered.
 
 class OrderedMapsTest {
   static testMain() {
     testMaps(const { "a": 1, "c": 2 }, const { "c": 2, "a": 1}, true);
     testMaps({ "a": 1, "c": 2 }, { "c": 2, "a": 1 }, false);
   }
 
   static void testMaps(map1, map2, bool isConst) {
     Expect.isFalse(identical(map1, map2));
@@ skipping 54 matching lines @@
 
     values = map1.values.toList();
     Expect.equals(3, values.length);
     Expect.equals(4, values[0]);
   }
 }
 
 main() {
   OrderedMapsTest.testMain();
 }