Here I found this website:
Chocolate Toxicity in Dogs
Semisweet chocolate has 150 mg/oz (528mg/100gm): toxic dose for 50 lb dog - 15 oz of semisweet chocolate
I'm pretty sure 1 chocolate chip is less than 1.5oz. (5 lb dog) A handful would be serious but 1 is OK. Just watch for an upset tummy.