Modifying already shared permissions for screen

[martinthomson]

@KiranKumarGuduru says:
Considering a use case where the use has provided permissions to share a part of the screen and now want to modify the permissions to share a full screan or vice versa for example, then it will be good to have a permission dialog, which displays an option like "modify existing permissions".

[martinthomson]

My current plan, which might not be shared by others, is to treat different windows as logically different sources. That requires new consent. And full screen will not be an option. That way, we can even expose application sharing to the drive-by web without running afoul of cross origin problems.

[martinthomson]

@KiranKumarGuduru says:
I agree to treat "different windows as different sources and to get new consent to access". I am not sure whether it is already mentioned in the draft, if not it is good to add this point.

The permission modification is not limited just to enhancing the consent to full screan.
For the usecase where the user has permitted to share a part of the window, and now want to modify the permission to shrink or extend the screen sharing part of the window (might not be even to full window), then modifications to existing consent is more userfriendly than that of acquiring a new cosent to that extend/ shrinked part and closing the existing consent.

[martinthomson]

Changes to source are not compatible with the spec; though implementations might choose to implement their own switcher, anything that touches the API will have to request a new share.