Rewrite fast/multicol/shadow-breaking.html as a check-layout test.

The old / current multicol implementation had imperfect column balancing in the
old test, so writing a reftest would be tricky, but anyway: it's not obvious
that our current behavior (both implementations) where we include the shadows
in the columns, rather than letting them overflow, is correct (as a matter of
fact, it's most likely wrong). So let's just test what really needs to work:
that a shadow doesn't incorrectly push the next line down.

BUG=386567
R=andersr@opera.com

Review URL: https://codereview.chromium.org/910313003

git-svn-id: svn://svn.chromium.org/blink/trunk@190085 bbb929c8-8fbe-4397-9dbb-9b2b20218538
14 files changed