[CSS Grid Layout] The 'auto' height must be adapted to the item's margin.

When using 'auto' on grid-template-{rows-columns} properties, the vertical
margin should be taken into account when computing the item's logical height,
so the grid container's height is adapted accordingly.

BUG=357419

Review URL: https://codereview.chromium.org/217113003

git-svn-id: svn://svn.chromium.org/blink/trunk@172302 bbb929c8-8fbe-4397-9dbb-9b2b20218538