Revert "Remove Expect from core library."

tests/language/top_level_var_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";
-
 
 var a, b;
 
 
 class TopLevelVarTest {
   static testMain() {
     Expect.equals(null, a);
     Expect.equals(null, b);
     a = b = 100;
     b++;
     Expect.equals(100, a);
     Expect.equals(101, b);
 
     Expect.equals(111, x);
     Expect.equals(112, y);
   }
 }
 
 
 // Ensure that initializers work for both const and non-const variables.
 const int x = 2 * 55 + 1;
 int y = x + 1;
 
 
 main() {
   TopLevelVarTest.testMain();
 }