[CSS Grid Layout] Cache several vectors to avoid malloc/free churn

[Sergio Villar Senin]

We should probably merge:

    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
    
    Review URL: https://chromiumcodereview.appspot.com/24331003

[Sergio Villar Senin]

I have a patch ready for this, but I won't upload it as it depends in another two patches already pending on review.

[Sergio Villar Senin]

Created attachment 217664 [details]
Patch

[Dean Jackson]

Comment on attachment 217664 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=217664&action=review

> Source/WebCore/ChangeLog:10
> +        Layouting the grid items means a lot of calls to

Laying-out

[Sergio Villar Senin]

Committed r159741: <http://trac.webkit.org/changeset/159741>