You really don't want to use anything abrasive on chrome. Chrome is a very thin layer...if you scratch it you're hosed. You do not actually abrasively polish chrome, you just clean it.
I've had quite good results with Nevr-Dull cotton wadding polish. It's a lot of work, but it'll take off a lot of crap and not damage the chrome. When I need to get more aggressive (or my hands get tired) I've used a rotary polisher with a microfiber bonnet and a polish specifically designed for chrome (I've been using Mother's).
If the chrome is pitted or worn through, not much you can do besides replate.
If you are asking about the trim around the glass it's not chrome, it's stainless and can be repolished. It's tough stuff though and takes some work - best done off the car on a polishing wheel with appropriate grades of rouge.
The louvered vent could be aluminum, which could be sanded and polished but it's more likely chrome and would have to be either replaced or re-plated. When chrome plating gets pitted it's done for.