Atlantic City casinos posted their first annual gaming revenue gains in a decade, and the credit is primarily due to their online gambling operations. Figures released Thursday by the New Jersey Division of Gaming Enforcement show the state’s seven surviving casinos generated brick-and-mortar gaming revenue of $189.7m in December, a 6.8% gain over December 2015. Throw in the $18.4m generated by state-licensed online gambling sites and the year-on-year gain rises to 8.6%. If you compare only the revenue generated by the seven casinos that were open to the public in both Decembers, the year-on-year brick-and-mortar gain rises to 13.6%, while…