Facebook, the top social networking site, will receive more than one in five online display ad dollars in the U.S. this year, and Google (GOOG) likely has nothing to fear from the Microsoft (MSFT) -Yahoo (YHOO) alliance, says a report released early Tuesday. In 2011, Facebook will get 21.6% of all online display ad dollars in the U.S., or $2.19 billion, says the report from research firm eMarketer. That percentage is up from 13.6% last year and 7.3% in 2009. Yahoo is expected to be No. 2, 16.4% of online display ad sales, followed by Google at 12.6% and AOL(AOL)...