Mark Zuckerberg, co-founder and chief executive officer of Facebook Inc., arrives to a Bloomberg television interview at Facebook headquarters in Menlo Park, California, U.S.,  on Tuesday, Dec. 2, 2014. Facebook made further headway in mobile in 2014, a business that has flourished from a minor portion of ad revenue at the time of the company's initial public offering to a majority. Photographer: David Paul Morris/Bloomberg via Getty Images