Function webkit2gtk_sys::webkit_cookie_manager_get_cookies_finish

pub unsafe extern "C" fn webkit_cookie_manager_get_cookies_finish(
    cookie_manager: *mut WebKitCookieManager, 
    result: *mut GAsyncResult, 
    error: *mut *mut GError
) -> *mut GList

This is supported on crate feature v2_20 only.