Fixing MutationObserver constructor from zones change

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 57b4bf831daea51987007bd7bf9589a2ec93a32f..77fd27463337590acfa2e8c32335ab28545eba83 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -17531,7 +17531,11 @@ class MutationObserver extends Interceptor native "MutationObserver,WebKitMutati
     return JS('MutationObserver',
         'new(window.MutationObserver||window.WebKitMutationObserver||'
         'window.MozMutationObserver)(#)',
-        convertDartClosureToJS(_wrapZone(callback), 2));
+        convertDartClosureToJS((changes, observer) {
+          _wrapZone(() {
+            callback(changes, observer);
+          });
+        }, 2));
   }
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file