Accept the new <box> value for CSS Shapes

The shape properties now accept box values [margin/border/padding/content]-box.
This patch parses the values and accepts them for layout for shape-outside.
Most of the work is done adjusting the size and offset of the box in ShapeInfo.

BUG=322165

Review URL: https://codereview.chromium.org/82403002

git-svn-id: svn://svn.chromium.org/blink/trunk@163193 bbb929c8-8fbe-4397-9dbb-9b2b20218538