Show a bubble mirror.
A Chrome App to capture your WebCam video feed in a tiny bubble during a screencast recording session on your ChromeBook.
Disclaimer: Dev Channel only for now!
This is easily achieved by combining the Dev Channel only app.window.alpha permission and app.window.alwaysOnTop permission.
And last, but not least, you can choose the Video Source in Context Menu options.
Check out public source at https://github.com/beaufortfrancois/bubble-mirror-chrome-app