Code review comment for lp:~brandontschaefer/mir/update-confined-region

This isn't a sufficient fix. For example:

  o in mir_demo_server fullscreen surfaces are resized when display resolutions are changed.
  o in mir_demo_server --window-manager tiling surfaces are resized when other sessions start/stop

I suggest adding an observer to the surface that updates the seat when resized_to() is called.