Revert "Remove Expect from core library."

tests/language/multi_pass2_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.
 // Dart test for loading several dart files and resolving superclasses lazily.
 // Same as MultiPassTest, except that the file order is reversed.
 
 library MultiPass2Test.dart;
-import "package:expect/expect.dart";
 part "multi_pass_a.dart";
 part "multi_pass_b.dart";
 
 
 class Base {
   Base(this.value) { }
   var value;
 }
 
 class MultiPass2Test {
   static testMain() {
     var a = new B(5);
     Expect.equals(5, a.value);
   }
 }
 
 main() {
   MultiPass2Test.testMain();
 }