The last time we checked on the support page of Google, is said to sync Gmail contacts with your iPhone, you should set up the account as a “CardDAV”. Today it still says the same thing, but Apple is the ingenuity to make the lives of their clients much easier and now offers Calendars and Contacts synchronization simply by turning a button on the second beta of iOS 7.
This new feature was discovered by an 9to5mac reader. For September 2012, Google added the CalDav protocol supported CardDAV and iOS. Back then it was not necessary because Exchange mode still worked relatively well. But Google made its Winter cleaning and annihilate the Exchange service for mobile users, then all iOS devices were affected, being forced to set up the account as CardDAV and CalDav.
However, Google still shows the same procedure on his support page. It is important to note that this should be treated as BETA and possibly reach or not the final version of iOS 7 coming in a couple month