[Passwords] Expose Touch To Fill in chrome://flags

This change adds the Touch To Fill flag to the list of UI flags and adds
corresponding metadata.

Bug: 957532
Change-Id: I4d366827140b6ba1f88903afec1755808c6ad1ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1675654
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672148}
5 files changed