Make private symbols non-enumerable

src/lookup.cc

Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index 256aa02d21cf4ffffc9487b0b2bbd6662bb07cb6..98aab68c6d94e345f7925cdf5d5a086b669cbf9d 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -308,6 +308,11 @@ void LookupIterator::PrepareTransitionToDataProperty(
     PropertyAttributes attributes, Object::StoreFromKeyed store_mode) {
   DCHECK(receiver.is_identical_to(GetStoreTarget()));
   if (state_ == TRANSITION) return;
+
+  if (!IsElement() && name()->IsPrivate()) {
+    attributes = static_cast<PropertyAttributes>(attributes | DONT_ENUM);
+  }
+
   DCHECK(state_ != LookupIterator::ACCESSOR ||
          (GetAccessors()->IsAccessorInfo() &&
           AccessorInfo::cast(*GetAccessors())->is_special_data_property()));
@@ -442,6 +447,9 @@ void LookupIterator::TransitionToAccessorProperty(
   // handled via a trap. Adding properties to primitive values is not
   // observable.
   Handle<JSObject> receiver = GetStoreTarget();
+  if (!IsElement() && name()->IsPrivate()) {
+    attributes = static_cast<PropertyAttributes>(attributes | DONT_ENUM);
+  }
 
   if (!IsElement() && !receiver->map()->is_dictionary_map()) {
     Handle<Map> old_map(receiver->map(), isolate_);