[CSS Grid Layout] Speed up painting of large grids with overflowing items

https://codereview.chromium.org/23439008 added a correctness
fallback for painting grids with items overflowing their grid
areas. That CL was effectively disabling all the painting
optimizations if the grid had just a single grid item overflowing
its grid area.

This patch tries to be smarter by tracking those grid items and
painting them whenever needed. Profiling of a big (200x200) grid
shows how the amount of time spent painting the grid decreases by
an order of magnitude, from 0.18% of total execution time to
0.01%.

BUG=248151

Review URL: https://codereview.chromium.org/98563003

git-svn-id: svn://svn.chromium.org/blink/trunk@166966 bbb929c8-8fbe-4397-9dbb-9b2b20218538