Fenced frames: Disable prefetch via "rel=prefetch" when Fenced Frame untrusted network is disabled.

Fenced Frame can disable its network by calling
`window.fence.disableUntrustedNetwork()`. After network is disabled,
no network requests are allowed from the fenced frame. Internally,
this is done by marking the fenced frame nonce, which is unique per
fenced frame, as disabled for network.

1. There is a check on the nonce of network request in
`CorsURLLoaderFactory::CreateLoaderAndStart`, which prevents new
requests with network disabled nonce.

2. There is also a check `CancelRequestIfNonceMatchesAndUrlNotExempted`.
It cancels in-progress network request whose nonce is disabled for
network.

With these two checks, attaching the fenced frame nonce to the
prefetch request will disable prefetch request when the FF network is
disabled.

Bug: 1515599
Change-Id: I3ae469db3de611c0bdb191237a827924b2e4f6df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5621950
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Xiaochen Zhou <xiaochenzh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1314704}