Revert "Remove Expect from core library."

tests/language/super_first_constructor_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.
 
-import "package:expect/expect.dart";
-
 // Test that the constructor body of a superclass is invoked.
 
 class Super {
   final superArgument;
   var superField;
 
   Super() : this.named(''); // Redirection is required to trigger the bug.
 
   Super.named(this.superArgument) {
     superField = 'fisk';
   }
 }
 
 class Sub extends Super {
   var subField;
 
   // Test for a bug when super() is the first initializer.
   Sub.first() : super(), subField = [];
 
   Sub.last() : subField = [], super();
 }
 
 main() {
   Expect.equals('fisk', new Sub.last().superField);
   Expect.equals('fisk', new Sub.first().superField);
 }