Revert "Remove Expect from core library."

tests/corelib/map_from_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 map.from.test;
-import "package:expect/expect.dart";
 import 'dart:collection';
 
 main() {
   testWithConstMap();
   testWithNonConstMap();
   testWithLinkedMap();
 }
 
 testWithConstMap() {
   var map = const { 'b': 42, 'a': 43 };
@@ skipping 55 matching lines @@
   var map = const { 'b': 1, 'a': 2, 'c': 3 };
   var otherMap = new LinkedHashMap.from(map);
   Expect.isTrue(otherMap is Map);
   Expect.isTrue(otherMap is! HashMap);
   Expect.isTrue(otherMap is LinkedHashMap);
   var i = 1;
   for (var val in map.values) {
     Expect.equals(i++, val);
   }
 }