lgtm. Pushed one suggestion/fixup.

Nice fixup;  I wondered about that and looked into the classinfo but never got as far as figuring out it doesn't get freed.

+       while (g_hash_table_iter_next (&hash_iter, (gpointer) &dbus_property_name, (gpointer) &variant)) {
+               g_variant_builder_add (&notifies, "{sv}",
+                                      dbus_property_name,
+                                      g_variant_ref (variant))

If I'm not mistaken, g_variant_build_add() calls g_variant_new() which
takes its own reference to @variant; so the g_variant_ref() is not
needed here.

(In reply to Beniamino Galvani from comment #3)
> +       while (g_hash_table_iter_next (&hash_iter, (gpointer)
> &dbus_property_name, (gpointer) &variant)) {
> +               g_variant_builder_add (&notifies, "{sv}",
> +                                      dbus_property_name,
> +                                      g_variant_ref (variant))
> 
> If I'm not mistaken, g_variant_build_add() calls g_variant_new() which
> takes its own reference to @variant; so the g_variant_ref() is not
> needed here.

You're entirely correct.  Fixed.

tested and merged to git master