Filter focus for buttons when there are overlays on top

Bug: 902427
Change-Id: Ida893cf41478976f4d3784091a79385db69ef1f0
Reviewed-on: https://chromium-review.googlesource.com/c/1324450
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606212}