Code review comment for lp:~alan-griffiths/mir/only-visible-surfaces-change-scene

This proposal makes sense for improved efficiency at least, but I'm not sure if it improves correctness at all...

Theoretically the compositor should be treated as something that may sample the scene at any time, at any frequency. So briefly drawing a frame when there's not really any new changes to show shouldn't be an error. Unless the shell is broken and fails to draw itself on start-up when there are no active clients(?).

Feels like we're missing the mark on addressing the root cause. But also feels like a worthy change to have...