Not to sound like I'm being a b****, but this is from the RMCA:
"Dr. Castiglione specifically suggested not feeding any baker's chocolate, or products such as homemade chocolate cake or frosting made with large quantities of baker's chocolate. I would assume that rats would not even want pure baker's chocolate as it is not sweet and even has an unpleasant flavor. Dr. Kean said that he could see no problem in giving a couple of semi-sweet chocolate chips, even on a daily basis, as long as the rat was receiving a nutritionally complete diet and the treat did not replace this diet."
In conclusion, I'm just worried.