AppDelegate.swift

import UIKit
// import文を追加する
import GoogleMobileAds

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {



    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Mobile Ads SDKを初期化する
        GADMobileAds.sharedInstance().start(completionHandler: nil)
        return true
    }
...