RenderGrid should include grid items' margins in its intrinsic size

RenderGrid should include grid items' margins in its intrinsic size

To match flexbox and the author's intent, the grid element's intrinsic
logical widths should account for the fixed margins on any grid items'.
The change is straightforward and moves the code from RenderFlexibleBox
to RenderBlock for easy sharing.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=158041

[eseidel, 2013-09-19 16:53:29]

lgtm

[commit-bot: I haz the power, 2013-09-19 16:53:43]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/24031007/1

[commit-bot: I haz the power, 2013-09-19 18:16:11]

Change committed as 158041