Do not leak private property names to proxy traps and interceptors.

src/lookup.cc

Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index 3b953c9d71f7f70f1c37ffc3d760740d8d316c2c..1ffd888350bda9c46c8b5b6de434edb4d8d74db0 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -610,6 +610,7 @@ LookupIterator::State LookupIterator::LookupInHolder(Map* const map,
   switch (state_) {
     case NOT_FOUND:
       if (map->IsJSProxyMap()) {
+        // Do not leak private property names.
         if (!name_.is_null() && name_->IsPrivate()) return NOT_FOUND;
         return JSPROXY;
       }
@@ -625,6 +626,8 @@ LookupIterator::State LookupIterator::LookupInHolder(Map* const map,
       }
       if (check_interceptor() && HasInterceptor(map) &&
           !SkipInterceptor(JSObject::cast(holder))) {
+        // Do not leak private property names.
+        if (!name_.is_null() && name_->IsPrivate()) return NOT_FOUND;
         return INTERCEPTOR;
       }
     // Fall through.