Revert "Remove Expect from core library."

tests/corelib/list_as_map_test.dart

 // Copyright (c) 2013, 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";
-
 void testListMapCorrespondence(List list, Map map) {
   Expect.equals(list.length, map.length);
   for (int i = 0; i < list.length; i++) {
     Expect.equals(list[i], map[i]);
   }
   Expect.isNull(map[list.length]);
   Expect.isNull(map[-1]);
 
   Iterable keys = map.keys;
   Iterable values = map.values;
@@ skipping 72 matching lines @@
   testConstAsMap(const [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
   testAsMap([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
   List list = new List(10);
   for (int i = 0; i < 10; i++) list[i] = i + 1;
   testFixedAsMap(list);
 
   testConstAsMap(const []);
   testAsMap([]);
   testFixedAsMap(new List(0));
 }