The WPT about inheritance of CSP for srcdoc iframes on history
navigations had been changed: first we wanted to always inherit CSP
from the parent, then we agreed to actually store the CSPs in history.
The comments on the test are still outdated and confusing, so let's
fix them.

Bug: 1329190
Change-Id: I366be21a1b845f2b22c1555874ae4433b57e6069
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3779760


Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Auto-Submit: Antonio Sartori <antoniosartori@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1028186}