[CSS Grid Layout] Avoid preferred logical widths' recomputations

[CSS Grid Layout] Avoid preferred logical widths' recomputations

The code runs the content-sized track sizing algorithm all the time,
which forces a layout even when the track is not content-sized. This
change makes us bail out if we know we don't need to run the
algorithm. Note that it will not help content sized grid tracks.

This speeds up PerformanceTests/Layout/fixed-grid-lots-of-data.html
from ~28.5 run/s to ~585 run/s by avoiding a lot of unneeded layouts.

The baselines change comes from triggering less layouts, which changes
the frame rects between 2 subsequent layouts thus changing the repaint
rectangles.

BUG=225892
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156028

[ojan, 2013-08-12 22:50:39]

lgtm

[commit-bot: I haz the power, 2013-08-12 22:51:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/22949002/1

[commit-bot: I haz the power, 2013-08-13 16:44:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/22949002/1

[commit-bot: I haz the power, 2013-08-13 16:44:56]

Change committed as 156028