Function fetch_a_single_imported_module_script 

fn fetch_a_single_imported_module_script(
    url: ServoUrl,
    owner: ModuleOwner,
    destination: Destination,
    options: ScriptFetchOptions,
    referrer: Referrer,
    on_complete: impl FnOnce(Option<Rc<ModuleTree>>) + 'static,
)

https://html.spec.whatwg.org/multipage/#fetch-a-single-imported-module-script