Add feature flag for Switch Access

Bug: 907179
Change-Id: I1f66d659690027191a5c2d0d21f09abb2f2d82d0
Reviewed-on: https://chromium-review.googlesource.com/c/1347575
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/master@{#610911}
12 files changed