Revert "Remove Expect from core library."

tests/compiler/dart2js_native/native_class_inheritance2_frog_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.
 
-import "package:expect/expect.dart";
-
 // Test to see if resolving a hidden native class's method interferes with
 // subsequent resolving the subclass's method.  This might happen if the
 // superclass caches the method in the prototype, so shadowing the dispatcher
 // stored on Object.prototype.
 
 class A native "*A" {
   foo([a=100]) native;
 }
 
 class B extends A native "*B" {
@@ skipping 54 matching lines @@
   Expect.equals('C.foo(300)', d.foo());
   // If the above line fails with C.foo(100) then the dispatch to fill in the
   // default got the wrong one, followed by a second dispatch that resolved to
   // the correct native method.
 
   Expect.equals('A.foo(1)', a.foo(1));
   Expect.equals('A.foo(2)', b.foo(2));
   Expect.equals('C.foo(3)', c.foo(3));
   Expect.equals('C.foo(4)', d.foo(4));
 }