Revert "Remove Expect from core library."

tests/language/type_variable_bounds2_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 of parameterized types with invalid bounds.
 
 abstract class J<T> { }
 
 abstract class K<T> { }
 
 abstract class I<T
   extends num /// 00: continued
   extends num /// 01: continued
   extends num /// 02: continued
@@ skipping 37 matching lines @@
     // In both production and checked modes, A<int> is a subtype of I.
     Expect.isTrue(a is I);
 
     // In both production and checked modes, A<int> is a subtype of J.
     Expect.isTrue(a is J);
 
     // In both production and checked modes, A<int> is not a subtype of K.
     Expect.isTrue(a is !K);
   }
 }