Revert "Remove Expect from core library."

tests/compiler/dart2js_native/native_method_with_keyword_name_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";
-
 // Make sure we can have a native with a name that is a JavaScript keyword.
 
 class A native "*A" {
   int delete() native;
 }
 
 A makeA() native { return new A(); }
 
 void setup() native """
 function A() {}
 A.prototype.delete = function() { return 87; };
 
 makeA = function(){return new A;};
 """;
 
 
 main() {
   setup();
 
   var a = makeA();
   Expect.equals(87, a.delete());
   A aa = a;
   Expect.equals(87, aa.delete());  
 }