Revert "Remove Expect from core library."

tests/compiler/dart2js_native/native_use_native_name_in_table_frog_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 that we put native names and not Dart names into the dynamic
 // dispatch table.
 
 class A native "*NativeA" {
   foo() native;
 }
 
 class B extends A native "*NativeB" {
 }
 
@@ skipping 27 matching lines @@
   var a = makeA();
   Expect.equals(42, a.foo());
   A aa = a;
   Expect.equals(42, aa.foo());  
 
   var b = makeB();
   Expect.equals(42, b.foo());
   B bb = b;
   Expect.equals(42, bb.foo());  
 }