Financial Times has a nice analysis of the deal -- it sounds like this agreement will help both sides, as Riot will not only get that nice cash infusion of a rumored $350 million, but also invaluable assistance and insight for what it was already hoping would be a nice overseas adoption. And Tencent, of course, gets to lay claim to League of Legends and any other titles that Riot developers, along with the huge microtransaction-based revenues that go along with them, both here and eventually overseas.
Plus, this is a sign of the growing trend of Eastern publishers picking up Western companies to develop content for the large audiences over there. Chinese publisher The9 recently bought another Blizzard spinoff, Red 5 Studios, for $15 million, and Japanese firm DeNA picked up iOS developer ngmoco for $400 million as well. Western audiences are big, but Eastern audiences are bigger and, as a result, there's high demand for well-developed games in that market.