Adding supported flag to HashChangeEvent.

tests/html/history_test.dart

Index: tests/html/history_test.dart
diff --git a/tests/html/history_test.dart b/tests/html/history_test.dart
index 211b950ee742922e44ba5913245703c05a132ff2..c3f017049204ee70fe5ff2b3c10fb50465e16d85 100644
--- a/tests/html/history_test.dart
+++ b/tests/html/history_test.dart
@@ -22,6 +22,12 @@ main() {
     });
   });
 
+  group('supported_HashChangeEvent', () {
+    test('supported', () {
+      expect(HashChangeEvent.supported, true);
+    });
+  });
+
   var expectation = History.supportsState ? returnsNormally : throws;
 
   group('history', () {
@@ -68,6 +74,7 @@ main() {
     });
 
     test('hashchangeevent', () {
+      var expectation = HashChangeEvent.supported ? returnsNormally : throws;
       expect(() {
         var event = new HashChangeEvent('change', oldUrl:'old', newUrl: 'new');
         expect(event is HashChangeEvent, true);