Fixing more cases of default values for events not working on Dartium.

tests/html/mutationobserver_test.dart

Index: tests/html/mutationobserver_test.dart
diff --git a/tests/html/mutationobserver_test.dart b/tests/html/mutationobserver_test.dart
index ef0d7d6391f37c4a81e108c0b470cee8f5ffbc1e..1886a57a28bb5bbfb9292a67705ec828d1b857ca 100644
--- a/tests/html/mutationobserver_test.dart
+++ b/tests/html/mutationobserver_test.dart
@@ -131,8 +131,13 @@ main() {
     });
 
     test('mutation event', () {
-      var event = new MutationEvent('something');
+      // Bug 8076 that not all optional params are optional in Dartium.
+      var event = new MutationEvent('something', prevValue: 'prev',
+          newValue: 'new', attrName: 'attr');
       expect(event is MutationEvent, isTrue);
+      expect(event.prevValue, 'prev');
+      expect(event.newValue, 'new');
+      expect(event.attrName, 'attr');
     });
   });
 }