- remove a couple of copies in the process
- need to use std::function instead of LINK to handle the unique_ptr

Change-Id: Ic760d2fc639bf2e11d5bddbfbb6f2d5f15b78fe3
Reviewed-on: https://gerrit.libreoffice.org/60397
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>