It's Safari-based, which is Webkit-based. Chrome is also Safari-based on iOS, because all the browsers must be. There's no actual Chrome (as in Blink, the browser engine) on iOS, at least in Play Store.
So I'm talking only about iOS. When I said it's Safari-based, I meant Webkit based, but I thought Firefox/Chrome actually pull parts of Safari on iOS. Quick research says that's wrong and they just use Webkit. Not an iOS dev, so someone can point out better sources for the 100% correct terminology.