Revert "Remove Expect from core library."

tests/language/ct_const_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.
 // All things regarding compile time constant expressions.
 
-import "package:expect/expect.dart";
-
 abstract class Roman {
   static const I = 1;
   static const II = 2;
   static const III = 3;
   static const IV = 4;
   static const V = 5;
 
   static const VivaItalia = const {"green": 1, "red": 3, "white": 2};
 }
 
@@ skipping 98 matching lines @@
     Expect.equals(true, caughtException);
     Expect.equals(1, c11dItaly["green"]);
 
     Expect.equals(true, null == naught);
   }
 }
 
 main() {
   CTConstTest.testMain();
 }