Right now this doesn't make any difference, since Bitmap is the
superclass of AlphaMask.
But when I switch to using alpha instead of transparency, passing
AlphaMask around is going to mean something different to passing plain
Bitmap around.
Change-Id: Ic1541e5f0a3b97331793cd23e23115faa7f382b0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/151463
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Noel Grandin
1c7cbd6856