Update unittest to new package layout.

pkg/unittest/lib/src/config.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.
 
 /** This file is sourced by unitest.dart. */
 
 /**
  * Hooks to configure the unittest library for different platforms. This class
  * implements the API in a platform-independent way. Tests that want to take
  * advantage of the platform can create a subclass and override methods from
@@ skipping 131 matching lines @@
   // Currently e.message works in dartium, but not in dartc.
   handleExternalError(e, String message) =>
       _reportTestError('$message\nCaught $e', '');
 
   _postMessage(String message) {
     // In dart2js browser tests, the JavaScript-based test controller
     // intercepts calls to print and listens for "secret" messages.
     print(message);
   }
 }