Use a private own symbol instead of a hidden property for hash codes

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index 600f312927e144bb20d93b7a6db72be2effe592c..0095e3385c94c5b454b0321d72b3df7352cda2a9 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -233,7 +233,7 @@ class Factory final {
   // Create a symbol.
   Handle<Symbol> NewSymbol();
   Handle<Symbol> NewPrivateSymbol();
-  Handle<Symbol> NewPrivateOwnSymbol();
+  Handle<Symbol> NewPrivateOwnSymbol(Handle<Object> name);
 
   // Create a global (but otherwise uninitialized) context.
   Handle<Context> NewNativeContext();