Custom state: Make the feature experimental state

Bug: 1012098
Change-Id: I266825bc3482fbc82c00fa9ef96d7b269c03a4fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1852345
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704560}