Add mediaId to PlaybackStateCompat extras

It provides a way to associate PlaybackState with the current media
item.

Startblock:
  <unknown commit> is submitted
PiperOrigin-RevId: 368354775

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

@@ -15,6 +15,7 @@
  */
  */
 package com.google.android.exoplayer2.ext.mediasession;
 package com.google.android.exoplayer2.ext.mediasession;
 
 
+import static androidx.media.utils.MediaConstants.PLAYBACK_STATE_EXTRAS_KEY_MEDIA_ID;
 import static com.google.android.exoplayer2.Player.EVENT_IS_PLAYING_CHANGED;
 import static com.google.android.exoplayer2.Player.EVENT_IS_PLAYING_CHANGED;
 import static com.google.android.exoplayer2.Player.EVENT_PLAYBACK_PARAMETERS_CHANGED;
 import static com.google.android.exoplayer2.Player.EVENT_PLAYBACK_PARAMETERS_CHANGED;
 import static com.google.android.exoplayer2.Player.EVENT_PLAYBACK_STATE_CHANGED;
 import static com.google.android.exoplayer2.Player.EVENT_PLAYBACK_STATE_CHANGED;
@@ -45,6 +46,7 @@ import com.google.android.exoplayer2.ControlDispatcher;
 import com.google.android.exoplayer2.DefaultControlDispatcher;
 import com.google.android.exoplayer2.DefaultControlDispatcher;
 import com.google.android.exoplayer2.ExoPlaybackException;
 import com.google.android.exoplayer2.ExoPlaybackException;
 import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
 import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
+import com.google.android.exoplayer2.MediaItem;
 import com.google.android.exoplayer2.Player;
 import com.google.android.exoplayer2.Player;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Assertions;
@@ -783,6 +785,10 @@ public final class MediaSessionConnector {
     float playbackSpeed = player.getPlaybackParameters().speed;
     float playbackSpeed = player.getPlaybackParameters().speed;
     extras.putFloat(EXTRAS_SPEED, playbackSpeed);
     extras.putFloat(EXTRAS_SPEED, playbackSpeed);
     float sessionPlaybackSpeed = player.isPlaying() ? playbackSpeed : 0f;
     float sessionPlaybackSpeed = player.isPlaying() ? playbackSpeed : 0f;
+    @Nullable MediaItem currentMediaItem = player.getCurrentMediaItem();
+    if (currentMediaItem != null && !MediaItem.DEFAULT_MEDIA_ID.equals(currentMediaItem.mediaId)) {
+      extras.putString(PLAYBACK_STATE_EXTRAS_KEY_MEDIA_ID, currentMediaItem.mediaId);
+    }
     builder
     builder
         .setActions(buildPrepareActions() | buildPlaybackActions(player))
         .setActions(buildPrepareActions() | buildPlaybackActions(player))
         .setActiveQueueItemId(activeQueueItemId)
         .setActiveQueueItemId(activeQueueItemId)