Revert "Remove Expect from core library."

tests/language/super_call3_test.dart

 // Copyright (c) 2011, 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 for testing implicit super calls with bad arguments or no default
 // constructor in super class.
 
-import "package:expect/expect.dart";
-
 class A {
   A(
     this.x  /// 01: compile-time error
   );
   final foo = 499;
 }
 
 class B extends A {}
 
 class B2 extends A {
@@ skipping 17 matching lines @@
 }
 
 main() {
   Expect.equals(499, new B().foo);
   Expect.equals(499, new B2().foo);
   Expect.equals(499, new B2.named().foo);
   Expect.equals(499, new D().foo);
   Expect.equals(499, new D2().foo);
   Expect.equals(499, new D2.named().foo);
 }