New positioning model: support for rounded rectangle shape-outside

Update the shape-outside rounded rectangle tests and import them from
the CSS WG's repository. They have been moved to the CSS WG repository
so they can be part of the spec test suite for CSS Shapes.

This is a port from WebKit: http://trac.webkit.org/changeset/153063

BUG=260357

Review URL: https://chromiumcodereview.appspot.com/20786002

git-svn-id: svn://svn.chromium.org/blink/trunk@155029 bbb929c8-8fbe-4397-9dbb-9b2b20218538