Code review comment for lp:~vanvugt/mir/unocclude

I wrote the texture cache logic in GLRenderer, so I know it behaves the same on any platform and that's not speculation.

The remaining point is whether uploading unused vertices is negligible for the number of surfaces on a desktop. I would argue after a while working on Compiz I got a good idea that yes, it is negligible. So that's a strongly educated guess rather than speculation.