How do I customize the title bar of a popup in a chrome extension?

Question

How do i style the title bar of a popup in a chrome extension? I notice this being done by Chat for Chrome. (Note: the screenshot for that one is outdated)

I got as

Answer 1

Turns out that this isn't a regular chrome extension I was looking at. It's a chrome packaged app. And it's possible to remove the title bars with chrome apps.