Convert fast/multicol/unsplittable-inline-block to reftest.

Removed explicit 'width' and shortened text lines to make the test
"compatible" with vertical-lr/rl.

R=mstensho@opera.com
BUG=386567

Review URL: https://codereview.chromium.org/698203003

git-svn-id: svn://svn.chromium.org/blink/trunk@184916 bbb929c8-8fbe-4397-9dbb-9b2b20218538