Revert "Remove Expect from core library."

tests/language/dynamic_test.dart

 // Copyright (c) 2012, 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.
 //
 // Dart test program testing the use of 'dynamic' in generic types.
 // @static-clean
 
-import "package:expect/expect.dart";
-
 abstract class Iface<K,V> {
 }
 
 class M1<K, V> implements Iface<K, V> {
 }
 
 class M2<K> implements Iface<K, dynamic> {
 }
 
 class M3 implements Iface<String, dynamic> {
@@ skipping 36 matching lines @@
   Expect.equals("dynamic", has_field.dynamic);
 
   HasMethodDynamic has_method = new HasMethodDynamic();
   Expect.equals("dynamic", has_method.dynamic());
 
   {
     int dynamic = 0;  // Local variable named dynamic is allowed.
     Expect.equals(0, dynamic);
   }
 }