All the crazy rumors splashing around September 2016 that Goggle had removed support for Chromecast from Linux Chromium was false it is a bug and a fix is supposed to be coming down the pipe.

After scouring the internet I found this instruction that worked for me and allowed Chromium to work with the casting extension.

1. In your Chromium browser go to chrome://flags#media-router and select “Disabled”.
2. Install Google Cast extension: https://chrome.google.com/webs…
3. Voila, now you can cast using the extension

I hope this helps someone.