tests: import unittest via package: url

tests/html/element_classes_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.
 
 library ElementTest;
-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:collection';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   Element makeElement() => new Element.tag('div');
 
   Element makeElementWithChildren() =>
     new Element.html("<div><br/><img/><input/></div>");
@@ skipping 310 matching lines @@
     document.documentElement.children.remove(listElement);
   });
 
   test('listContainsAll', () {
     var elements = listElementSetup();
     expect(elements.classes.containsAll(['qux', 'meta', 'mornin']), isFalse);
     expect(elements.classes.containsAll(['qux', 'lassy', 'classy']), isTrue);
     document.documentElement.children.remove(listElement);
   });
 }