Add support for parsing <grid-line> that includes a 'span'

Add support for parsing <grid-line> that includes a 'span'

This adds the parsing, style resolution and getComputedStyle bits
to our code. The rendering code was not made aware of the new type
of GridPosition yet.

BUG=229713
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=148766

[ojan, 2013-04-11 02:44:46]

https://codereview.chromium.org/13992003/diff/1/LayoutTests/fast/css-grid-lay...
File LayoutTests/fast/css-grid-layout/grid-item-start-before-get-set.html
(right):

https://codereview.chromium.org/13992003/diff/1/LayoutTests/fast/css-grid-lay...
LayoutTests/fast/css-grid-layout/grid-item-start-before-get-set.html:125:
shouldBe("getComputedStyle(element, '').getPropertyValue('-webkit-grid-row')",
"'span 20 / auto'");
This, and the other cases where both grid-lines specify a span, don't seem to
match the spec. 

"If opposing grid-placement properties both specify a grid span, they both
compute to ‘auto’."

Am I misreading it?

[Julien - ping for review, 2013-04-17 14:26:26]

https://codereview.chromium.org/13992003/diff/1/LayoutTests/fast/css-grid-lay...
File LayoutTests/fast/css-grid-layout/grid-item-start-before-get-set.html
(right):

https://codereview.chromium.org/13992003/diff/1/LayoutTests/fast/css-grid-lay...
LayoutTests/fast/css-grid-layout/grid-item-start-before-get-set.html:125:
shouldBe("getComputedStyle(element, '').getPropertyValue('-webkit-grid-row')",
"'span 20 / auto'");
> Am I misreading it?

You are not! I thought we could get away with doing the computation in
RenderGrid but we wouldn't match the right 'computed value' so this needs to be
changed.

[Julien - ping for review, 2013-04-17 20:58:46]

Updated the change and the tests to match the specification. The main change is
that we add a hook in StyleResolver::adjustRenderStyle to handle the 2 'span'
case.

[ojan, 2013-04-17 22:39:53]

lgtm

[commit-bot: I haz the power, 2013-04-19 21:31:58]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/13992003/5001

[commit-bot: I haz the power, 2013-04-19 22:05:43]

Retried try job too often on linux_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_layo...

[Julien - ping for review, 2013-04-19 23:18:58]

Committed patchset #2 manually as r148766 (presubmit successful).