I'm pretty sure it's a teaspoon of hydrogen peroxide that will make the dog hurl.
I wouldn't worry about it TOO much, try to wait and see what the vet says, although if he doesn't get back to you quickly, you may want to go ahead and get the dog to yack. I don't think there's any reason *not* to. (Some poisons, you don't want coming back up, but reading a few sites online it doesn't look like this is an issue with chocolate and dogs, the general concensus is "induce vomiting."
AFAIK, the deal with chocolate and dogs is that there is some compound similar to caffiene in it that dogs just can't deal with. HOWEVER the "good" news is that your average sweet candy chocolate doesn't have NEARLY as much as a dark unsweetened chocolate.