Can someone tell me what these are?

If you decide to paint it, like monochromatic (body color) a good epoxy etch primer will be what you need to use otherwise nothing will stick to it, that and sanding the chrome with a DA sander to rough it up to get the epoxy to stick.

Additionally though welding the slots is preferred, if you dont have access to a welder, grind the slots slightly concave, and sand them on the sides of the slotted holes to clean rust free steel, tape it from the back, and fill the slots solid with JB weld. Then sand it smooth, epoxy prime the bumper, and then further work the filled areas with sandpaper and some fine scratch and pinhole filler like evercoat.

Then scuff the epoxy primer down, and apply your filler primer, sand it smooth and topcoat the bumper with your body color.