Remove opaque origin verification exception from NoStatePrefetch.

NoStatePrefetchProcessorImpl::Start() validates the initiator_origin_
using ChildProcessSecurityPolicy::HostsOrigin(), but it currently only
does so if the initiator_origin_ is not opaque. HostsOrigin() can now
handle opaque origins correctly, including checking their precursor,
and can also enforce tighter rules for sandboxed frame processes. It
shouldn't be necessary to skip opaque checks at this point, so this CL
enables opaque origin checking behind a kill switch (shared among a few
other places that had similar opaque origin escape hatches).

Change-Id: I313cba26bd2a0d4928d4af14b867418777d5324f
Bug: 40109437, 325410297
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5588515


Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312930}