[CSS Grid Layout] Speed up content sized track layout

[CSS Grid Layout] Speed up content sized track layout

This change narrows down the relayout condition in
RenderGrid::logicalContentHeightForChild to only
percentage children: as they are the only lengths that
depends on the containing block's override. We
unfortunately can't use percentHeightDescendants as
it's not populated yet. This code can probably be
simplified further down but it's a good start.

This greatly speeds up the new performance test, moving
from 25 runs/sec to 91 runs/sec.

BUG=234211
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156122

[ojan, 2013-08-13 17:22:21]

https://codereview.chromium.org/22983004/diff/1/Source/core/rendering/RenderG...
File Source/core/rendering/RenderGrid.cpp (right):

https://codereview.chromium.org/22983004/diff/1/Source/core/rendering/RenderG...
Source/core/rendering/RenderGrid.cpp:512: if
(child->style()->logicalHeight().isPercent())
What if it's position:absolute; top:0; bottom: 0? Does that not also hit this?
Do we get that case wrong today?

[Julien - ping for review, 2013-08-13 18:45:42]

https://codereview.chromium.org/22983004/diff/1/Source/core/rendering/RenderG...
File Source/core/rendering/RenderGrid.cpp (right):

https://codereview.chromium.org/22983004/diff/1/Source/core/rendering/RenderG...
Source/core/rendering/RenderGrid.cpp:512: if
(child->style()->logicalHeight().isPercent())
On 2013/08/13 17:22:21, ojan wrote:
> What if it's position:absolute; top:0; bottom: 0? Does that not also hit this?

Absolutely positioned grid items don't participate in the layout per the
specification (http://dev.w3.org/csswg/css-grid/#abspos-items)

> Do we get that case wrong today?

I am pretty sure we don't handle that properly due to lack of testing around
absolutely positioned grid items.

[ojan, 2013-08-14 21:56:34]

lgtm

[commit-bot: I haz the power, 2013-08-14 21:56:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/22983004/1

[commit-bot: I haz the power, 2013-08-14 23:21:12]

Change committed as 156122