[content picking] Content picking mode does not reflect the current app that requires picking

[Rachel Liu]

Current situation
Picking mode gets confused when you are already in picking mode for Edit Contacts then go to System settings background change.

1. Contacts app --> Edit --> icon for picking profile pic
2. In content picking mode for Contacts app (selected a picture but not confirmed)
3. Go to Dash and launch System settings
4. System --> select 'Change' to choose background
5. Picking mode reflects Contacts app not System background change. If you change to another picture and confirm with 'Pick' it takes you back to Address book with the profile picture updated instead of System background app

Desired solution
Each app should be associated with it's own content picking mode so it doesn't get confused.

[Michał Sawicz (saviq)]

This needs more investigation on the desired solution, but will most probably require support for parented windows in mir / unity-mir as well as changes in unity8.

[Michał Sawicz (saviq)]

We do have prompt sessions in unity8 now, supporting the use case of multiple picker sessions.

I don't think there's anything more unity8 has to do here, it's the content hub that needs to make use of the trusted prompt mechanism.

Reopen if you think otherwise.