Layout support for new circle shape syntax

Implement support for doing layout with the new circle shape syntax,
including basic animation support.

Add a few tests for the new circle syntax. The old tests in
LayoutTests/csswg will be removed when the old syntax is removed.

Also update existing shape-inside, animation, and clip-path tests to
test the new syntax.

Patch by Bem Jones-Bey.

BUG=322165

Review URL: https://codereview.chromium.org/115253003

git-svn-id: svn://svn.chromium.org/blink/trunk@164731 bbb929c8-8fbe-4397-9dbb-9b2b20218538