Facebook was Zynga’s path to glory — the Facebook game FarmVille, a virtual agribusiness, put the San Francisco social-gaming company on the map. But since its $7 billion IPO in 2011, Zynga has been having a rough time of it, culminating in the axing of 520 employees, or 18 percent of its workforce, last month. On July 1, the job cuts reached founding CEO Mark Pincus, who will be replaced by former Microsoft Xbox chief Don Mattrick. (Pincus will stay on as chief products officer.) The change was enough to boost Zynga’s stock a bit, but on Thursday the company…