Revert "Remove Expect from core library."

tests/standalone/medium_integer_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.
 // Testing Mints. Note that the tests may not work on 64-bit machines,
 // as Smi's would be used to represent many of the numbers.
 
 library MediumIntegerTest;
-import "package:expect/expect.dart";
 
 
 class MediumIntegerTest {
 
   static int getMint() {
     return 1234567890123456789;
   }
 
   static testSmiOverflow() {
      int a = 1073741823;
@@ skipping 86 matching lines @@
     Expect.equals(false, a.hashCode == b.hashCode);
     Expect.equals(true, a.hashCode == (b - 1).hashCode);
   }
 }
 
 main() {
   for (int i = 0; i < 4000; i++) {
     MediumIntegerTest.testMain();
   }
 }