Code review comment for lp:~kdub/mir/overlay-gl-program

What is being rendered is "overlay rejects" and once rejected by the hwc, there is nothing "overlay" about them. These renderables should no longer be considered overlays, and the code to render them should not be called a name with the word "overlay" in it (unless it's overlay_rejects or smth that makes it clear that they are not overlays) for the sake of clarity. I see that there is code that already made it in, like render_gl_and_overlays, which I think is confusing and should be cleaned up in time.

For these rejects, I think it'd be nice to find a way to fall back to the usual path (I know you had some concerns about it, though). This may be a good time to factor things out of GLRenderer to make it reuseable. But I don't have an issue with a little bit of duplication if we want to wait for "role clarity", as Alan put it.