"Not now" means exactly what it says: The user hasn't made a decision about whether to allow or deny yet. After the user selects it, they can reopen the popup that asked for the permission (by clicking on the little video icon, which sticks around if that option is chosen) and choose whether to grant it or not.
Basically, clicking "Not now" is exactly the same as the following user actions:
- In Firefox, just clicking outside the popup that comes up on your fiddle. That dismisses the popup, without selecting any of the options.
- In Chrome, simply ignoring the infobar that's requesting the permission and not clicking anything at all in it.
and your code should handle it just like it handles those user actions.