Fix handling of 'inherit' and 'initial' for grid lines

Fix handling of 'inherit' and 'initial' for grid lines

'initial' and 'inherit' are always allowed values for CSS properties.
As the CSSParser handles them automatically, those 2 values were never
taken care of in StyleResolver, leading to ASSERTs triggering.

While touching this code, renamed the RenderStyle grid line accessors
as it shouldn't ambiguous to whom they apply.

BUG=234198
TESTS=fast/css-grid-layout/grid-item-column-row-get-set.html
      fast/css-grid-layout/grid-item-end-after-get-set.html
      fast/css-grid-layout/grid-item-start-before-get-set.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=149257

[eseidel, 2013-04-27 08:55:41]

lgtm

[commit-bot: I haz the power, 2013-04-27 08:55:55]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/14493016/3001

[commit-bot: I haz the power, 2013-04-27 09:01:58]

Change committed as 149257