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 77fd27463337590acfa2e8c32335ab28545eba83..83f6fbf1321d144eae60e65a00ff0bb75c37be71 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -17531,11 +17531,7 @@ class MutationObserver extends Interceptor native "MutationObserver,WebKitMutati
     return JS('MutationObserver',
         'new(window.MutationObserver||window.WebKitMutationObserver||'
         'window.MozMutationObserver)(#)',
-        convertDartClosureToJS((changes, observer) {
-          _wrapZone(() {
-            callback(changes, observer);
-          });
-        }, 2));
+        convertDartClosureToJS(_wrapBinaryZone(callback), 2));
   }
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
@@ -33417,6 +33413,11 @@ _wrapZone(callback) {
   return Zone.current.bindUnaryCallback(callback, runGuarded: true);
 }
 
+_wrapBinaryZone(callback) {
+  if (Zone.current == Zone.ROOT) return callback;
+  return Zone.current.bindBinaryCallback(callback, runGuarded: true);
+}
+
 Element query(String selector) => document.query(selector);
 ElementList queryAll(String selector) => document.queryAll(selector);
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file