Facebook’s website has been blocked for over a decade in China, while its CEO Mark Zuckerberg has gone from would-be friend of Beijing to one of its leading critics in Silicon Valley. Even so, the social media giant has discovered a highly lucrative way to make money from Chinese advertisers. Facebook now generates more than $5 billion a year in revenue from China, according to an estimate from Brian Wieser, an analyst at equity research firm Pivotal Research — all with apparent Chinese government approval.  Its strategy involves targeting the country’s most ambitious advertisers, such as game designers, e-commerce giants, app creators and government entities. The result is mutually beneficial: Facebook gets some access to the Chinese market, while Chinese companies can reach international audiences.  The company, though, is still tight-lipped about its business in China — perhaps because this apparent "win-win" cooperation has meant Facebook doing business w