Calculate border-box dimensions correctly for cells

When constraining a height on a cell according to box sizing we need to exclude the intrinsic
padding on table cells (calculated to line up the content of the cells with the
baseline of its neighbours) but include any collapsed borders the cells have
picked up from the row/table.

BUG=627305

Review-Url: https://codereview.chromium.org/2148513002
Cr-Commit-Position: refs/heads/master@{#406775}
15 files changed