[New Multicolumn] Leave remaining disabled test disabled, and explain why.

[New Multicolumn] Leave remaining disabled test disabled, and explain why.

I've gone through all interesting multicol tests that needed to be converted to
reftests, js-tests (or at least something that isn't dump-render-tree or PNG
tests).

The remaining tests either provide no additional test coverage, or are invalid (albeit
passing in the old implementation), so just keep them disabled. Will be removed once
the old multicol implementation is gone (that's crbug.com/408123).

BUG=386567
R=rune@opera.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=192340

[rune, 2015-03-23 07:58:57]

lgtm

[mstensho (USE GERRIT), 2015-03-23 08:41:36]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-03-23 08:41:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1023203002/1

[commit-bot: I haz the power, 2015-03-23 10:02:23]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=192340