Revert "Remove Expect from core library."

tests/language/int_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.
 // Test basic integer operations.
 
-import "package:expect/expect.dart";
-
 class IntTest {
   static void testMain() {
     Expect.equals(0, 0 + 0);
     Expect.equals(1, 1 + 0);
     Expect.equals(2, 1 + 1);
     Expect.equals(3, -1 + 4);
     Expect.equals(3, 4 + -1);
 
     Expect.equals(1, 1 - 0);
     Expect.equals(0, 1 - 1);
@@ skipping 32 matching lines @@
     Expect.equals(7, (7).remainder(-9));
     Expect.equals(7, (7).remainder(9));
     Expect.equals(-7, (-7).remainder(-9));
   }
 }
 
 
 main() {
   IntTest.testMain();
 }