title: Notifications not showing on Oreo emulator
body: <p>I have been trying to show a simple notification on an Oreo emulator. Strangely, I see nothing.</p>
  
  <p>Let's eliminate obvious answers: I tried to check the notifications for the app, I tried the Notifications and the NotificationCompat path. I tried with or without channels, I tried with or without groups.</p>
  
  <p>The code is elementary (yes, I use Kotlin but it's easy to understand):</p>
  
  <pre><code>class MainActivity : Activity() {
  
  var id = 0
  
  override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      val button:View = findViewById(R.id.button)
      button.setOnClickListener(this::onAddNotification)
  }
  
  private fun onAddNotification(v: View) {
      id++
      val builder = Notification.Builder(this).setSmallIcon(R.drawable.ic_notifications_none)
              .setContentTitle("Content #$id").setContentText("Content text for $id")
  
      val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
      notificationManager.notify(id, builder.build())
  }
  }
  </code></pre>
  
  <p>Needless to say that it's code that works perfectly on pre-Oreo. On the other hand, Gmail and Maps show notifications on that emulator.
  Anything I might have forgotten?</p>
  
  <p>Thanks</p>