On Linux, Chrome uses GTK.  GTK+, or the GIMP Toolkit, is a multi-platform toolkit for creating graphical user interfaces. Offering a complete set of widgets, GTK+ is suitable for projects ranging from small one-off tools to complete application suites.

Today, the team removed the GTK+ port of Chrome, replacing it with Aura, Google’s own project. Delete the GTK+ port of Chrome, the commit log said.

Aura for Linux is currently in beta. If you want to test Aura now, François Beaufort has a little tutorial here. If you want to know more about Aura, here is the official documentation.