Google’s settlement with the U.S. Justice Department will cost the company $500 million. The search giant acknowledged that its ads improperly helped Canadian online pharmacies to sell controlled drugs in the United States without requiring a prescription, as well as counterfeit drugs. The amount of the settlement wasn’t plucked out of thin air; it represents the gross revenue that Google received from the Canadian pharmacies, plus the gross revenue the pharmacies received from their sales to consumers across the border, during the period from 2003 to 2009. The Justice Department argued that G…