using unittest via package import

tests/html/request_animation_frame_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 RequestAnimationFrameTest;
-import '../../pkg/unittest/lib/unittest.dart';
-import '../../pkg/unittest/lib/html_config.dart';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   test('oneShot', () {
       var frame = window.requestAnimationFrame(
           expectAsync((timestamp) { }));
     });
 
@@ skipping 28 matching lines @@
           expectAsync((timestamp1) { }));
       var frame2 = window.requestAnimationFrame(
           (timestamp2) {
             throw new Exception('Should have been cancelled');
           });
       var frame3 = window.requestAnimationFrame(
           expectAsync((timestamp3) { }));
       window.cancelAnimationFrame(frame2);
     });
 }