Individual WPT tests for each backdrop-filter

This CL adds a specific, individual WPT test for each type of
backdrop-filter effect.

If you find yourself here, looking for the test for blur() or
a multi-filter (combined) test, see crbug.com/978481.

Bug: 831485
Change-Id: I065fd94dbfe5ef0813ffe90f07878247147d3261
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674708
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672131}
21 files changed