Resolve percent lengths for abs. positioned tables against padding box.

According to CSS2.1: "[...] absolutely positioned elements whose
containing block is based on a block container element, the percentage
is calculated with respect to the width of the padding box of that
element".

BUG=366123

Review URL: https://codereview.chromium.org/341523002

git-svn-id: svn://svn.chromium.org/blink/trunk@177101 bbb929c8-8fbe-4397-9dbb-9b2b20218538