Change description:
Add CSS3 nav-up/down/left/right properties and focus control support to allow 
CSS3 UI navigation for targeted devices.

Changes to API surface:
This is an internal change that doesn't change the API surface but it changes existing behavior of spatial navigation if CSS3 nav-* properties are used.

Links:
Spec - http://dev.w3.org/csswg/css-ui/#nav-dir
The www-style discussion on the feature:
http://lists.w3.org/Archives/Public/www-style/2013Jun/0332.html

Support in other browsers:
Internet Explorer: N/A
Firefox: N/A
Safari: N/A
Opera: In device-targeted products