Enable sharedStorage.get() in network-restricted fenced frames.

If the proper flag (kFencedFramesLocalUnpartitionedDataAccess) is
enabled, sharedStorage.get() can now be called in fenced frames.
The call will only succeed if the entire tree rooted at the fenced
frame has disabled untrusted network access, including nested
fenced frames trees.

Bug: 324440086
Change-Id: Ie6788ba6d299a334800ecf11ba90151eaf40f43d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5279221


Reviewed-by: Cammie Smith Barnes <cammie@chromium.org>
Reviewed-by: Ben Kelly <wanderview@chromium.org>
Commit-Queue: Andrew Verge <averge@chromium.org>
Reviewed-by: Garrett Tanzer <gtanzer@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1272982}