Adding more layout/WPT tests for backdrop-filter

These should reproduce (at least) these issues:
 - https://crbug.com/622128 - dark areas brought in from edges
 - https://crbug.com/632979 - dark areas brought in from edges
 - https://crbug.com/659501 - menus cause too much filtering
 - https://crbug.com/767997 - menus cause too much filtering
 - https://crbug.com/813796 - incorrect border used for filter
 - https://crbug.com/593307 - incorrect border used for filter

Bug: 497522,622128,632979,659501,767997,813796,593307
Change-Id: Iafea2fc8fffba950f74d27f21170df647dc62e29
Reviewed-on: https://chromium-review.googlesource.com/c/1330888
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608537}
16 files changed