Spec: https://fetch.spec.whatwg.org/#ref-for-cross-origin-resource-policy-internal-check
This purpose of this patch is just to implement the spec.
One noticeable thing I did in the patch is I made `CacheResponse` to
include the `credentials mode` of the initial request. Consider the
below scenario:
1. Create a fetch request with a URL and a specific credential_mode, and put it into cache
2. Call cache.match by using a URL, but without credential_mode
3. cache.match() result should be filtered according to the initial request's credential_mode
When applying the `response’s request-includes-credentials is true`
check, the initial request's `credential_mode` is needed because
`request-includes-credentials` is judged by the `credential_mode`.
The rest of the changes are just normal spec alignments.
Differential Revision: https://phabricator.services.mozilla.com/D147803
4a4cbd8e23