Bug 1596391 - Fix silly boolean logic mistake. r=bustage a=dluca

    fn flattened_tree_parent_is_parent(&self) -> bool {

        use crate::gecko_bindings::structs::*;

        let flags = self.flags();

        if !self.is_in_shadow_tree() {

        // FIXME(emilio): The shadow tree condition seems it shouldn't be needed

        // anymore, if we check for slots.

        if self.is_in_shadow_tree() {

            return false;

        }