Allow grid positions to be named grid areas

Allow grid positions to be named grid areas

This change extends our handling of grid position to allow for
named grid areas. This required to split the shorthands parsing
between grid-{row|column} and grid-area as the rules for expanding
are slightly different.  The patch reuses a lot of the existing logic
to marshall the values into RenderStyle.

One big difference after this change is that:

grid-row: foobar / none;

used to be rejected at parsing but is now allowed.

BUG=258092
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=155555

[darktears, 2013-08-05 21:07:42]

On 2013/08/05 20:45:08, Julien Chaffraix wrote:

LGTM

[commit-bot: I haz the power, 2013-08-05 21:09:46]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/22215002/1

[commit-bot: I haz the power, 2013-08-06 00:03:55]

Change committed as 155555