[CSS Grid Layout] Heap-buffer-overflow in std::sort()

r179621 added support to handle infinite sizes to the
sortByGridTrackGrowthPotential() sorting function. The problem is that it broke
the strict weak ordering required by std::sort when the compared items had both
infinite maximum sizes, so the algorithm was going nuts.

BUG=401983, 402508, 402757

Review URL: https://codereview.chromium.org/493093002

git-svn-id: svn://svn.chromium.org/blink/trunk@181634 bbb929c8-8fbe-4397-9dbb-9b2b20218538