Revert "Remove Expect from core library."

tests/language/top_level_func_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 testing top-level variables.
 
-import "package:expect/expect.dart";
-
 
 class TopLevelFuncTest {
   static testMain() {
     var z = [1, 10, 100, 1000];
     Expect.equals(Sum(z), 1111);
 
     var w = Window;
     Expect.equals(w, "window");
 
     Expect.equals(null, rgb);
@@ skipping 35 matching lines @@
 }
 
 Function get Enumerator {
   int k = 0;
   return () => k++;
 }
 
 main() {
   TopLevelFuncTest.testMain();
 }