Improve cover scaling to app/output scale factor.
@carlosg
Submitted by Carlos Garnacho Link to original bug (#774402)
Description
Right now gnome-music is doing a cairo->pixbuf->cairo conversion on every cover just to get a cairo surface with the right scale factor applied. This can be improved by using Gdk.Window.create_similar_image_surface(), so the first cairo surface has already the right device scale.
Patches coming.