Zynga Inc. is revamping its stock structure to grant the shares owned by Chief Executive Officer Mark Pincus 70 times more voting power than shares sold in its planned initial public offering. The board approved three tiers of stock, giving each one of Pincus's shares 70 votes, up from 10, according to a document obtained by Bloomberg. Pre-IPO investors and other current holders will get seven votes a share, up from one. Public investors will get one vote for each share.