Allow page to use camera only this time in Chrome/Chromium?

In Chrome/Chromium (version 50+), if, for instance, Hangouts asks me about webcam first time, the choice it proposes has only two options (to either forbid or allow), and when I press "Allow", browser remembers that as the permanent choice, that I have to un-do it manualy through the settings if I want to be asked about this next time.

Can I somehow allow the page to use my webcam only this time, without making it a permanent exception?