Revert "Remove Expect from core library."

tests/language/instanceof2_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";
-
 abstract class I { }
 
 abstract class AI implements I { }
 
 class A implements AI {
   const A();
 }
 
 class B implements I {
   const B();
@@ skipping 80 matching lines @@
   }
 }
 
 main() {
   // Repeat type checks so that inlined tests can be tested as well.
   for (int i = 0; i < 5; i++) {
     InstanceofTest.testMain();
   }
 }