It’s been a trying year for Facebook and perhaps one of the most challenging in the career of its COO. The social networking giant has been at the center of a seemingly never-ending stream of controversies, leading to a day of congressional grilling for Sandberg, who is now tasked with preventing more data privacy blunders and repairing Facebook’s reputation. The bright side: Facebook’s core online ad business continues to boom, and hot properties like Instagram could make up for its tepid user growth.