glic: Exclude X-Glic headers from CORS checks

This header is logically being added by the user agent (like client
hints and other things) and shouldn't require
Access-Control-Allow-Headers (which might require a CORS preflight
request).

I previously intended to limit this to same-origin requests, but it
turns out to be somewhat inconvenient to determine this from the
webRequest API. We could move this to a C++ interceptor, but this is
easier and should avoid the known CORS issues.

Bug: b:444266707

Change-Id: Ib39a62b63fd84e68f8c332c8ab434e63a486548d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6969974
Reviewed-by: Dan Harrington <harringtond@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1518258}