UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36

Steps to reproduce the problem:
Make a Chrome extension and try to make a frameless window.

What is the expected behavior?

What went wrong?
It can't be done.

WebStore page: 

Did this work before? No 

Chrome version: 51.0.2704.103  Channel: n/a
OS Version: OS X 10.11.6
Flash Version: Shockwave Flash 22.0 r0

It's possible for a Chrome extension author to do `chrome.windows.create({ type: 'popup' })` to make a window with no location bar or other browser chrome. But it still has a title bar, so your options for customising the UI are limited.

Currently, you can have a frameless popup by making a Chrome app, or you can have browser integration (tabs, history, etc.) by making a Chrome extension, but you can't have both.

Use case: an extension with a browser action that creates a frameless HUD-style popup window (which auto-closes once interacted with), something like Spotlight or Alfred but for searching within your open tabs or history.

I suggest a new CreateType, named something like "frameless_popup", which creates a popup with no title bar etc. This window would also be allowed to use the -webkit-app-region CSS property to make a draggable region, as documented here: https://developer.chrome.com/apps/app_window

Existing CreateTypes, for reference: https://developer.chrome.com/extensions/windows#type-CreateType