Although the algorithm for sizing tracks (rows or columns) is defined
once for both dimensions in the specification
(https://www.w3.org/TR/css-grid-2/#algo-track-sizing), we have
implemented it twice separately for sizing rows and columns.
In addition to code duplication, another issue is that these
implementations of the same algorithm have already diverged in some
places, and this divergence is likely to become even worse as our
implementation evolves.
This change unifies code for both dimension into one method that runs
track sizing.
While this change brings a bit of collateral damange (border.html and
minmax.html got changes in layout snaphots) it ultimately brings more
benefits because now we can evolve layout for both rows and colums
without duplicating the code :)
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