In China, Silicon Valley giants confront new walls

Shanghai

FACEBOOK is the world's largest social network, with more than two billion users. LinkedIn was sold to Microsoft for US$26 billion last year. And Apple is Apple, the most valuable company in the world.

In most local markets, it would be a surprise if any one of these companies were floundering. But in China, the real shock is that their troubles no longer surprise anyone.

Just in the past few weeks, one of Facebook's most popular apps was blocked by the …