Revert "Remove Expect from core library."

tests/language/getter_closure_execution_order_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.
 //
 // Test that a getter is evaluated after the arguments, when a getter is
 // for invoking a method. See chapter 'Method Invocation' in specification.
 
-import "package:expect/expect.dart";
-
 var counter = 0;
 
 class Test1 {
   get a {
     Expect.equals(1, counter);
     counter++;
     return (c) { };
   }
 
   b() {
@@ skipping 60 matching lines @@
     failures.add(stack);
   }
   // If any of the tests failed print out the details and fail the test.
   if (failures.length != 0) {
     for (var msg in failures) {
       print(msg.toString());
     }
     throw "${failures.length ~/ 2} tests failed.";
   }
 }