Add was_checkbox_visible boolean to OnUnmaskPromptAccepted.

Use was_checkbox_visible boolean in the if statement when set
kAutofillCreditCardFidoAuthOfferCheckboxState value.

Bug: b:288942439
Change-Id: Ic5f0c9a0906dbad790acd8436a260a8f6e17027e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5085027
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Reviewed-by: Vinny Persky <vinnypersky@google.com>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Olivia Saul <jsaul@google.com>
Commit-Queue: Longsheng Yin <longsheng@google.com>
Cr-Commit-Position: refs/heads/main@{#1235856}