What should I do if my chihuahua licked some chocolate?

Here is a website that calculates the risk: PetMD Chocolate Toxicity Meter According to this, a 4 lb. dog that ingested 0.2 oz of dark chocolate will have very mild symptoms, and you should keep an eye on him/her for GI upset, vomiting, or shaking. More serious indications would be tremors, seizures, hyperactivity, or racing heartbeat. (Note that I rounded down on weight and up on amount ingested when converting to U.S. units to see worst case). So you are probably OK, and I would guess that any symptoms would have shown up by now.