Revert "Remove Expect from core library."

tests/language/bit_operations_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 for testing bitwise operations.
 
-import "package:expect/expect.dart";
-
 class BitOperationsTest {
   static testMain() {
     for (int i = 0; i < 4; i++) {
       testOne();
     }
   }
   static testOne() {
     Expect.equals(3, (3 & 7));
     Expect.equals(7, (3 | 7));
     Expect.equals(4, (3 ^ 7));
@@ skipping 151 matching lines @@
     }
   }
 
   static int ShiftLeft(int a, int b) { return a << b; }
   static int ShiftRight(int a, int b) { return a >> b; }
 }
 
 main() {
   BitOperationsTest.testMain();
 }