Revert "Remove Expect from core library."

tests/language/super_implicit_closure_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 program for testing invocation of implicit closures.
 
-import "package:expect/expect.dart";
-
 class BaseClass {
   BaseClass(this._i) {}
   int foo() { return _i; }
   int _i;
 }
 
 class DerivedClass extends BaseClass {
   DerivedClass(this._y, int j) : super(j) {}
   int foo() { return _y; }
   getSuper() { return super.foo; }
   int _y;
 }
 
 class SuperImplicitClosureTest {
   static void testMain() {
     DerivedClass obj = new DerivedClass(20, 10);
 
     var ib = obj.foo;
     Expect.equals(obj._y, ib());
 
     ib = obj.getSuper();
     Expect.equals(obj._i, ib());
   }
 }
 
 
 main() {
   SuperImplicitClosureTest.testMain();
 }