I dont think that will happen ...unless facebook's only interest is to make bucket loads of money. If China does end up buying stake in fb, fb risks loosing a lot of existing users.
Aren't they a corporation? What other interest would they have?
And Facebook is probably going to lose quite a few users to Google+ anyway - I can't think of anyone who would eschew Google+ for Facebook, but then suddenly quit because China invested.
Also: Many Chinese are accustomed to considerable collusion and shady dealings among partners. Simply publicizing a stake could make many Chinese leery of FB, and less likely to use it politically.