Bug 239624

According to the discussion on https://github.com/whatwg/html/issues/1142 (draft Spec PR https://github.com/whatwg/html/pull/7799), error events on <link rel=preload> should be fired only for network errors. WPT: https://github.com/web-platform-tests/wpt/pull/33382 On Safari, load events should be fired for responses that are not network errors (actual behavior: error events): - <link rel=preload as=style/script> + HTTP 404 (all browsers) - <link rel=preload as=image> + broken images (all browsers) error events should be fired for network errors (actual behavior: load events): - `<link rel=preload as=script>` + MIME type listed in https://fetch.spec.whatwg.org/#should-response-to-request-be-blocked-due-to-mime-type?, without nosniff (Safari/Chrome) Note: the events described above are on <link rel=preload>, which can be different from events fired on main requests e.g. <img>.