Check for CCT before using new security indicator

This exempts custom tabs from the new security indicator experiment.

Bug: 1245733
Change-Id: I73c3982d6a13164f2818aac408f81cfa1954c982
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3137315


Reviewed-by: Matt Jones <mdjones@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Commit-Queue: Chris Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/main@{#919275}