Fixing MutationObserver constructor from zones change

tools/dom/templates/html/impl/impl_MutationObserver.darttemplate

Index: tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate b/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
index bc036b44e8385692b351282d4ca97c9baedb22a3..48d7ae9ff16fa5761c19116f5a0af6333f131d13 100644
--- a/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
+++ b/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
@@ -84,10 +84,18 @@ $if DART2JS
     return JS('MutationObserver',
         'new(window.MutationObserver||window.WebKitMutationObserver||'
         'window.MozMutationObserver)(#)',
-        convertDartClosureToJS(_wrapZone(callback), 2));
+        convertDartClosureToJS((changes, observer) {
+          _wrapZone(() {
+            callback(changes, observer);
+          });
+        }, 2));
   }
 $else
   factory MutationObserver(MutationCallback callback) =>
-      new MutationObserver._(_wrapZone(callback));
+      new MutationObserver._((changes, observer) {
+        _wrapZone(() {
+            callback(changes, observer);
+          });
+        });
 $endif
 }