Comment 1 for bug 195832

I've added this, but there seems to be some issues. Or more precise, it works splendidly if not for the fact that if there's a normal frame rendering sandwiched between two icon render ops, the area outside the current viewport will contain strange data. It seems as if there's either a bug which causes this behaviour, or it's intended behaviour and I've misunderstood how the Viewports work when applied to a render texture. It needs more investigation. All code is committed, but currently deactivated.