Remove filter touch event when obscured on most of the buttons

We may just want to filter security buttons instead of all the buttons
since based on user feedback, screen filter apps are popular, and
filtering most buttons becomes a user pain.

Bug: 928715
Change-Id: I82abec5b428299d1a86207e8c21b66288b6b009a
Reviewed-on: https://chromium-review.googlesource.com/c/1454229
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629195}