[zoom-for-dsf] Scale focus ring by zoom.

Mac only. For consistency with previous versions.

See here for the changes in test expectations:
https://test-results.appspot.com/data/layout_results/mac-rel/741375/blink_web_tests%20%28retry%20shards%20with%20patch%29/layout-test-results/results.html

Bug: 1218722
Change-Id: Idf506161f011a73fcc92ea680aefb5592325d962
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3041885


Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Auto-Submit: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#906340}