Hacker News Reader

Not sure about in the phone, but in the desktop versions, you can click the (i)/Secure icon to the left of the website to review/change your permissions for the site.

For mobile, it looks like you can hit the vertical menu button in the top right, then the (i) icon, then Site Settings...

View on HN

The example site provided ( https://greggman.github.io/doodles/html5-webcam-iframe.html ) serves an iframe from a different domain so the site settings on the visible page do not affect the actual camera permissions:

Site settings: http://imgur.com/a/JIDeD (note: camera is set to 'block', but there is still the red dot in tab indicating camera access)

Camera usage: http://imgur.com/a/3HXHo (note: different domain listed)

Reply on news.ycombinator.com