[Sheriff-o-matic] Use before content hax to hide category labels instead of ever-present spans

[Sheriff-o-matic] Use before content hax to hide category labels instead of ever-present spans

This isn't an ideal solution, but it hides the failure category labels when there are
no failure cards. Also adding a bit of styling in the meantime.

NOTRY=true
TBR=ojan@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181597

[leviw_travelin_and_unemployed, 2014-09-09 03:12:27]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2014-09-09 03:12:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/leviw@chromium.org/555493005/20001

[commit-bot: I haz the power, 2014-09-09 03:13:12]

Committed patchset #2 (id:20001) as 181597