[layoutng] Add border and padding when setting the override size

This is necessary to avoid a DCHECK when opening the DOM inspector on
any page (and is also clearly correct)

R=mstensho@chromium.org,eae@chromium.org
BUG=635619

Review-Url: https://codereview.chromium.org/2360793002
Cr-Commit-Position: refs/heads/master@{#420480}
1 file changed