Help app: Add flags to correctly show content for allowed features.

Bug: b/321865996
Change-Id: I8a3bfa4582b019c5bc0bcee92795b6b9e69930a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401299


Reviewed-by: Zufeng Wang <zufeng@google.com>
Commit-Queue: Callistus Tan <callistus@google.com>
Cr-Commit-Position: refs/heads/main@{#1279498}