Remove Expect from core library.

tests/compiler/dart2js_foreign/foreign_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";
 import 'native_metadata.dart';
 
 foreign1(var a, var b) {
   return JS("num", r"# + #", a, b);
 }
 
 var called = false;
 callOnce() {
   Expect.isFalse(called);
   called = true;
   return 499;
 }
 
 foreign2() {
   var t = callOnce();
   return JS("num", r"# + #", t, t);
 }
 
 foreign11(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11) {
   return JS("num", r"# + # + # + # + # + # + # + # + # + # + #",
       a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11);
 }
 
 void main() {
   Expect.equals(9, foreign1(4, 5));
   Expect.equals(998, foreign2());
   Expect.equals('1234567891011',
       foreign11('1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11'));
 }