The U.S. Justice Department Friday approved Google's 400 million dollar acquisition of Admeld, a company that provides an online advertising platform for publishers.The Justice Department concluded that it was "not likely to substantially lessen competition in the sale of display advertising."Google operates the largest Internet search engine in the world and one of the largest display advertising platforms. It had revenues of about 29 billion dollars in 2010, most of which came from ads revenue.Admeld, with annual revenue of 30 million dollars, offers technology services to Internet publishers that help them boost revenue by optimizing ads display from hundreds of sources.Google is expected to grab 9.3 percent of online display advertising spending in the U.S. this year, up from 8.6 percent last year, making it the No. 3 provider, according to the digital intelligence company Emarketer.The No. 1 position will be taken by Facebook with its share increased to 16 percent up from 12 percent a year ago, while Yahoo! will slip slightly to 13 percent, said Emarketer.