Views which cannot be painted by the renderer
The following discussion from !582 (merged) should be addressed:
Hmmmm. My first thought was: every paint node should have a valid transform ensured when adding it to the z-order list, so this should be an assert. But I guess this can fail for legitimate reasons in future when we have more complex CM, so it shouldn't be an assert. But in that case, shouldn't we paint some kind of solid colour rather than just punching through to potentially garbage? Same for gl-renderer.