Revert "Remove Expect from core library."

tests/language/generic_instanceof3_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 for testing the instanceof operation.
 
-import "package:expect/expect.dart";
-
 // Tests involving generics.
 
 abstract class I<T> {
 }
 
 
 class A implements I<bool> {
 }
 
 
@@ skipping 34 matching lines @@
     Expect.isFalse(c is K<String>);
     Expect.isFalse(c is K<String>);
     Expect.isTrue(c is L<String>);
     Expect.isFalse(c is L<bool>);
     Expect.isTrue(c is K<bool>);
     Expect.isFalse(c is K<String>);
     Expect.isFalse(d is I<String>);
     Expect.isTrue(d is I<bool>);
   }
 }