Cache several vectors to avoid malloc/free churn

Cache several vectors to avoid malloc/free churn

distributeSpaceToTracks and
resolveContentBasedTrackSizingFunctionsForItems are both
called in a loop during layout and resulted in a lot of
mallocs / frees calls. This change just keeps their Vectors
around until the end of Layout, keeping the memory around.

This is a classic runtime vs memory trade-off as we will hold
onto the biggest allocation until the end of layout, which
should be fine as we *have* to allocate that amount.

This code refactors the often passed-in arguments & the cached
Vectors into a new data structure GridSizingData. This makes
the code cleaner while making it difficult to forget free'ing
the memory at the end of layout.

This is a 40% improvement on auto-grid-lots-of-data.html.

BUG=273238
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=158228

[Z_DONOTUSE, 2013-09-23 23:49:21]

lgtm

[commit-bot: I haz the power, 2013-09-23 23:51:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/24331003/1

[commit-bot: I haz the power, 2013-09-24 01:25:22]

Change committed as 158228