ExtendDirtyRegion
fDirtyInfo.ExtendDirtyRegion(top, bottom);
void ExtendDirtyRegion(int32 top, int32 bottom)
info.ExtendDirtyRegion(visibleDirtyTop, visibleDirtyBottom);
ExtendDirtyRegion(region, *dirty);
virtual void ExtendDirtyRegion(Region region, BRegion& dirty);