Don Mattrick, the former head of Microsoft’s entertainment division who takes the reins as chief executive officer of Zynga on Monday, has been hankering to run all or part of the social-gaming company for at least three years. In 2010, Mattrick negotiated with Zynga founder Mark Pincus about buying the maker of such popular games as “FarmVille,” according to people with knowledge of the matter. The idea was to bolster Microsoft’s Xbox lineup with social games that then were adding millions of users on Facebook’s network each week. The discussions ultimately fell apart, said the people, who asked not to be identified because the talks were private. Now, Mattrick, 49, is taking over Zynga from Pincus after the company lost its spot as the top game maker on Facebook to King.com.