Code review comment for lp:~albaguirre/mir/fix-1475571

Oh I see. It's probably the bo_flags getting GBM_BO_USE_SCANOUT due to the size of the surface (which is a very ugly heuristic). With the SCANOUT flag, gbm will refuse RGBA and only allow RGBX. That's spurious because we actually have no desire for scan-out support in screencasting and there might be a real alpha channel that we want.

I think if gbm_bo_create throws adequate errors still then this change is fine. Providing it passes CI.