Ask HN: What widget toolkit does Chrome OS use?

I'm not familiar with Chrome/ium OS but recent news about applications on the OS getting a facelift caught my interest (http://thenextweb.com/dd/2016/04/20/googles-chrome-os-material-design/)

I'd like to know what widget toolkit they use to draw their user interface and if its viable for GUI development for other native non-Chrome OS applications.