Convert fast/multicol/flipped-blocks-border-after to reftest.

R=mstensho@opera.com
BUG=386567

Review URL: https://codereview.chromium.org/669603003

git-svn-id: svn://svn.chromium.org/blink/trunk@184248 bbb929c8-8fbe-4397-9dbb-9b2b20218538