Revert "Remove Expect from core library."

tests/language/namer_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";
-
 // Regression test for a bug in dart2js where global names could
 // collide.
 
 var i = 'top level';
 
 var i0 = 'top level zero';
 
 var i00 = 'top level zero zero';
 
 var i2 = 'top level too';
@@ skipping 39 matching lines @@
   Expect.equals('top level too', j2);
   Expect.equals('top level zero', j0);
   Expect.equals('B', B.j);
 
   Expect.equals('top level too', k2);
   Expect.equals('top level zero', k0);
   Expect.equals('top level', k);
   Expect.equals('C', C.k);
   Expect.equals('top level zero zero', k00);
 }