Function fetch_a_module_worker_script_graph 

pub(crate) fn fetch_a_module_worker_script_graph(
    cx: &mut JSContext,
    global: &GlobalScope,
    url: ServoUrl,
    fetch_client: ModuleFetchClient,
    destination: Destination,
    referrer: Referrer,
    credentials_mode: CredentialsMode,
    on_complete: impl FnOnce(&mut JSContext, Option<Rc<ModuleTree>>) + Clone + 'static,
)

https://html.spec.whatwg.org/multipage/#fetch-a-module-worker-script-tree https://html.spec.whatwg.org/multipage/#fetch-a-worklet/module-worker-script-graph