Revert "Remove Expect from core library."

tests/language/equality_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";
-
 
 class A {
   bool _result;
   A(this._result);
   operator ==(x) { return _result; }
 }
 
 
 opaque(x) => [x,1,'y'][0];  // confuse the optimizers.
 
@@ skipping 31 matching lines @@
   }
   if (death() != nullFn()) {
   } else {
     throw "failed";
   }
 }
 
 main() {
   for (int i = 0; i < 1000; i++) tests();
 }