Skip three region-based multicol tests that don't work with compositing

These tests don't work properly when compositing mode is enabled and are
blocking the effort to delete the non-compositing mode from Blink.

R=ojan@chromium.org
BUG=364960

Review URL: https://codereview.chromium.org/243533004

git-svn-id: svn://svn.chromium.org/blink/trunk@171980 bbb929c8-8fbe-4397-9dbb-9b2b20218538