Adding test & annotations for popstatevent.

tests/html/history_test.dart

 library HistoryTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 /// Waits for a callback once, then removes the event handler.
 void expectAsync1Once(EventListenerList list, void callback(arg)) {
   var fn = null;
   fn = expectAsync1((arg) {
     list.remove(fn);
@@ skipping 55 matching lines @@
     test('replaceState', () {
       expect(() {
         var length = window.history.length;
 
         window.history.replaceState(null, document.title, '?foo=baz');
         expect(window.history.length, length);
         expect(window.location.href.endsWith('foo=baz'), isTrue);
       }, expectation);
     });
 
+    test('popstatevent', () {
+      expect(() {
+        var event = new Event.eventType('PopStateEvent', 'popstate');
+        expect(event is PopStateEvent, true);
+      }, expectation);
+    });
+
     test('hashchangeevent', () {
       var expectation = HashChangeEvent.supported ? returnsNormally : throws;
       expect(() {
         var event = new HashChangeEvent('change', oldUrl:'old', newUrl: 'new');
         expect(event is HashChangeEvent, true);
         expect(event.oldUrl, 'old');
         expect(event.newUrl, 'new');
       }, expectation);
     });
   });
 }