Reuters: Nielsen announced on Wednesday that it is partnering with Tencent Holdings to measure its digital audience in a move that could direct more ad dollars from companies in the United States to China’s biggest social network. Nielsen said it is launching its Digital Ad Ratings, which tracks unique users, reach and frequency of a digital ad across computers, tablets and smartphones for the first time in China. Comscore, which offers a similar service and competes with Nielsen, said it is already available in China.