[fetch] Option to require response.ok (#103)

Something like:

```js
fetch(url, {
  requiredStatus: 'ok'
})
```

…which would cause `fetch` to reject if `response.ok` is false. Default value would be `any`. It could be a boolean, but a value like this means we could let the developer require a specific status code.

This would always reject with no-cors requests to avoid x-origin leakage.

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/103