Move unittest from lib to pkg.

tests/html/transferables_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.
 
 #library('TransferableTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
+#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
 
   test('TransferableTest', () {
     window.on.message.add(expectAsync1((messageEvent) {
       expect(messageEvent.data, new isInstanceOf<ArrayBuffer>());
     }));
     final buffer = (new Float32Array(3)).buffer;
     window.webkitPostMessage(buffer, '*', [buffer]);
   });
 }