[PrivacyPolicy] Screenshot tests

100 runs mac: https://ci.chromium.org/ui/inv/u-chrstne-2024-10-22-16-30-00-4ab911af54a34e9f/test-results?sortby=&groupby=&q=privacysandbox+

100 runs win: https://ci.chromium.org/ui/inv/u-chrstne-2024-10-22-16-38-00-9f225c5b131283a6/test-results?sortby=&groupby=&q=privacysandboxdialog+

100 runs linux: https://ci.chromium.org/ui/inv/u-chrstne-2024-10-22-16-52-00-8cfed141cbf14b21/test-results?sortby=&groupby=&q=privacysandboxdialog+

Change-Id: I93f1d3b9cf9c94756eca6def65c11299f4ca4725
Bug: 368310146
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5937991
Reviewed-by: Abe Boujane <boujane@google.com>
Reviewed-by: Jacob Stanley <jacobstanley@google.com>
Commit-Queue: Christine Ying <chrstne@google.com>
Cr-Commit-Position: refs/heads/main@{#1373959}