I had problems with the new Chromecast Cast option in Chrome and apparently it is because Google is rolling out a new way to cast that does not require the Google Chromecast extension. I found it much more annoying to have a blue cast window in the middle of my browser and half the time it could not even see my chromecast.
To downgrade you need to:
Enter
chrome://flags/
and turn off this setting: Media Router -> DISABLED
Reboot Chrome and it should work like it did before.
Also works on Chromebooks.