The investment was made by Google itself, not Google Ventures, say our sources, and it’s a highly strategic deal. Zynga will be the cornerstone of a new Google Games to launch later this year, say multiple sources. Not only will Zynga’s games give Google Games a solid base of social games to build on, but it will also give Google the beginning of a true social graph as users log into Google to play the games. And I wouldn’t be surprised to see PayPal being replaced with Google Checkout as the primary payment option. Zynga is supposedly PayPal’s biggest single customer, and Google is always looking for ways to make Google Checkout relevant.