Revert "Remove Expect from core library."

tests/corelib/big_integer_vm_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 Bigints.
 // TODO(srdjan): Make sure the numbers are Bigint and not Mint or Smi.
 
 library big_integer_test;
-import "package:expect/expect.dart";
 
 class BigIntegerTest {
 
   static foo() {
     return 1234567890123456789;
   }
 
   static testSmiOverflow() {
     var a = 1073741823;
     var b = 1073741822;
@@ skipping 151 matching lines @@
     var a = 10000000000000000000;
     var b = 10000000000000000001;
     Expect.equals(false, a.hashCode == b.hashCode);
     Expect.equals(true, a.hashCode == (b - 1).hashCode);
   }
 }
 
 main() {
   BigIntegerTest.testMain();
 }