[Passwords] Add pixel tests for all generation experiment arms

Bug: 326949412
Change-Id: I2e6d13315ccc78fb57272232df97879ee88dcad4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5323506


Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Commit-Queue: Rafał Godlewski <rgod@google.com>
Cr-Commit-Position: refs/heads/main@{#1265933}