The master tracking bug for implementing CSS3 Grid Layout.
This looks like it might be a duplicate of https://bugs.webkit.org/show_bug.cgi?id=58349
*** Bug 58349 has been marked as a duplicate of this bug. ***
*** Bug 72220 has been marked as a duplicate of this bug. ***
The spec: http://dev.w3.org/csswg/css3-grid-layout/