Update the backdrop-filter test corresponding to Backdrop Root
This test only tested a single case (opacity), and with a value
that is very close to 1.0 which could be skipped in some
implementation optimizations. I refactored the test into a set
of tests, one per Backdrop Root trigger. In the process, I
discovered that Blink doesn't correctly create a Backdrop Root
for two types of will-change value (see crbug.com/338250112).
Bug: 338250112
Change-Id: Id59c159c96c64250700aa05c00cc222aa3fac6ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5500001
Auto-Submit: Mason Freed masonf@chromium.org
Reviewed-by: Chris Harrelson chrishtr@chromium.org
Commit-Queue: Chris Harrelson chrishtr@chromium.org
Cr-Commit-Position: refs/heads/main@{#1295543}