call stop(true) when media action stop is received

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=205377624

extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/DefaultPlaybackController.java

 /*
- * Copyright (c) 2017 The Android Open Source Project
+ * Copyright (C) 2017 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -127,7 +127,7 @@ public class DefaultPlaybackController implements MediaSessionConnector.Playback
 
   @Override
   public void onStop(Player player) {
-    player.stop();
+    player.stop(true);
   }
 
   @Override

extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java

@@ -689,13 +689,16 @@ public final class MediaSessionConnector {
 
     @Override
     public MediaMetadataCompat getMetadata(Player player) {
+      if (player.getCurrentTimeline().isEmpty()) {
+        return null;
+      }
       MediaMetadataCompat.Builder builder = new MediaMetadataCompat.Builder();
-      if (player != null && player.isPlayingAd()) {
+      if (player.isPlayingAd()) {
         builder.putLong(MediaMetadataCompat.METADATA_KEY_ADVERTISEMENT, 1);
       }
       builder.putLong(
           MediaMetadataCompat.METADATA_KEY_DURATION,
-          player == null ? 0 : player.getDuration() == C.TIME_UNSET ? -1 : player.getDuration());
+          player.getDuration() == C.TIME_UNSET ? -1 : player.getDuration());
       long activeQueueItemId = mediaController.getPlaybackState().getActiveQueueItemId();
       if (activeQueueItemId != MediaSessionCompat.QueueItem.UNKNOWN_ID) {
         List<MediaSessionCompat.QueueItem> queue = mediaController.getQueue();