using unittest via package import

tests/html/hidden_dom_1_test.dart

 library HiddenDom1Test;
-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';
 
 // Test that the dart:html API does not leak native jsdom methods:
 //   onfocus setter.
 
 main() {
   useHtmlConfiguration();
 
   test('test1', () {
     document.body.children.add(new Element.html(r'''
@@ skipping 22 matching lines @@
   try {
     action();
   } catch (e) {
     ex = e;
   }
   if (ex == null)
     expect(false, isTrue, reason: 'Action should have thrown exception');
 
   expect(ex, isNoSuchMethodError);
 }