Revert "Remove Expect from core library."

tests/language/type_variable_field_initializer_test.dart

 // Copyright (c) 2013, 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.
 
 // Check that an inlined field initializer has access to the enclosing
 // type variables.
 
-import "package:expect/expect.dart";
-
 class A<T> {
   var c = new List<T>();
 }
 
 class B<T> extends A<T> {
 }
 
 main() {
   Expect.isTrue(new B<int>().c is List<int>);
   Expect.isFalse(new B<String>().c is List<int>);
 }