title: Unresolved reference adview, adrequest, mobileads
body: <p>I'm getting an issue in my Android project with Admob.
  I added the dependency <code>implementation 'com.google.android.gms:play-services-ads:17.1.2'</code> and the project builds normally, but (in development time) Android Studio cannot resolve any reference.</p>
  
  <p><code>import com.google.android.gms.ads.AdRequest (Unresolved reference: AdRequest)
  import com.google.android.gms.ads.AdView (Unresolved reference: AdView)
  import com.google.android.gms.ads.MobileAds (Unresolved reference: MobileAds)</code></p>
  
  <p>I'm using Android Studio 3.2.1, Kotlin plugin 1.3.11, compileSdkVersion 27, minSdkVersion 15.</p>
  
  <p>Have you ever faced something like that? How could I solve it?</p>