Adding supported flag to HashChangeEvent.

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);
     callback(arg);
   });
   list.add(fn);
 }
 
 main() {
   useHtmlIndividualConfiguration();
 
   group('supported_state', () {
     test('supportsState', () {
       expect(History.supportsState, true);
     });
   });
 
+  group('supported_HashChangeEvent', () {
+    test('supported', () {
+      expect(HashChangeEvent.supported, true);
+    });
+  });
+
   var expectation = History.supportsState ? returnsNormally : throws;
 
   group('history', () {
     test('pushState', () {
       expect(() {
         window.history.pushState(null, document.title, '?dummy');
         var length = window.history.length;
 
         window.history.pushState(null, document.title, '?foo=bar');
 
@@ skipping 26 matching lines @@
       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('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);
     });
   });
 }