Revert "Remove Expect from core library."

tests/language/unqual_name_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 program to check that we can resolve unqualified identifiers
 
-import "package:expect/expect.dart";
-
 
 class B {
   B(x, y) : b = y { }
   var b;
 
   get_b() {
     // Resolving unqualified instance method.
     return really_really_get_it();
   }
 
@@ skipping 16 matching lines @@
 
     // Check whether we handle variable initializers correctly.
     var a = 1, x, b = a + 3;
     Expect.equals(5, a + b);
   }
 }
 
 main() {
   UnqualNameTest.testMain();
 }