Set 3pc toggle visibility to false for TP UI on clank.

This is a temporary fix in the meantime as I am submitting CLs that are
for the TP UI but are before the button CL. With the existing logic
since the toggle isn't explicitly set to false, and in all the
screenshot tests there's a toggle at the bottom (like this:
https://screenshot.googleplex.com/BDBNRWMDdEnnEVM.png). This will be
resolved once the button CL goes in but in the interim this change will
prevent any UI weirdness in the screenshot tests.

Change-Id: Ia4517ab258e0b44447360b7d17f87bbb1c01c58c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6578467
Reviewed-by: Fiona Macintosh <fmacintosh@google.com>
Commit-Queue: Fiona Macintosh <fmacintosh@google.com>
Cr-Commit-Position: refs/heads/main@{#1464848}