Revert "Remove Expect from core library."

tests/compiler/dart2js_extra/hash_code_test.dart

 // Copyright (c) 2012, 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.
 
-import "package:expect/expect.dart";
-
 // dart2js specific test to make sure hashCode on intercepted types behaves as
 // intended.
 
 
 class Hasher {
   confuse(x) => [1, 'x', true, null, x].last;
   hash(x) => confuse(x).hashCode;
 }
 
 // Hashing via [hash] should be forced to use the general interceptor, but the
@@ skipping 57 matching lines @@
   Expect.equals(0x0DB819B, 'b'.hashCode);
   Expect.equals(0xEBA5D59, 'c'.hashCode);
 }
 
 main() {
   bools();
   ints();
   lists();
   strings();
 }