Remove Expect from core library.

tests/corelib/map_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_test;
+import "package:expect/expect.dart";
 import 'dart:collection';
 
 void main() {
   test(new HashMap());
   test(new LinkedHashMap());
   test(new SplayTreeMap());
   test(new SplayTreeMap(Comparable.compare));
   testLinkedHashMap();
   testMapLiteral();
   testNullValue();
@@ skipping 342 matching lines @@
 
   var count = 0;
   map.forEach((key, value) {
     if (key.isNaN) count++;
   });
   Expect.equals(2, count);
 
   map.clear();
   Expect.isTrue(map.isEmpty);
 }