Code review comment for lp:~kdub/mir/post-if-optimizable

I thought that we were migrating the basic GL composition pass down into DisplayBuffer? So that if your scene is expressible exclusively in terms of a RenderableList then you can just dump it into render_and_post_update() and the DisplayBuffer will either GL or overlay?

This would satisfy the ‘needs no negotiation’ criterion, and would seem to make the higher levels a little bit less complex?