Rename shapeSize and others to make ShapeInfo and friends easier to understand

The ShapeInfo hierarchy has grown organically as the spec has changed,
and the naming has become very stale and confusing. The spec is now in
Last Call, so it seems like a good time to take a stab towards better
naming that matches the spec terminology and is also more consistent in
general.

R=leviw@chromium.org

BUG=322165

Review URL: https://codereview.chromium.org/185393015

git-svn-id: svn://svn.chromium.org/blink/trunk@168409 bbb929c8-8fbe-4397-9dbb-9b2b20218538