Use serialized listener notification for all listener notifications.

This ensures that all callbacks use the same notification mechanism.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=222226913

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -238,8 +238,8 @@ import java.util.concurrent.CopyOnWriteArraySet;
     }
     if (this.playWhenReady != playWhenReady) {
       this.playWhenReady = playWhenReady;
-      notifyListeners(
+      int playbackState = playbackInfo.playbackState;
-          new PlayWhenReadyUpdate(listeners, playWhenReady, playbackInfo.playbackState));
+      notifyListeners(listener -> listener.onPlayerStateChanged(playWhenReady, playbackState));
     }
   }
 
@@ -253,9 +253,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
     if (this.repeatMode != repeatMode) {
       this.repeatMode = repeatMode;
       internalPlayer.setRepeatMode(repeatMode);
-      for (Player.EventListener listener : listeners) {
+      notifyListeners(listener -> listener.onRepeatModeChanged(repeatMode));
-        listener.onRepeatModeChanged(repeatMode);
-      }
     }
   }
 
@@ -269,9 +267,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
     if (this.shuffleModeEnabled != shuffleModeEnabled) {
       this.shuffleModeEnabled = shuffleModeEnabled;
       internalPlayer.setShuffleModeEnabled(shuffleModeEnabled);
-      for (Player.EventListener listener : listeners) {
+      notifyListeners(listener -> listener.onShuffleModeEnabledChanged(shuffleModeEnabled));
-        listener.onShuffleModeEnabledChanged(shuffleModeEnabled);
-      }
     }
   }
 
@@ -320,9 +316,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
       maskingPeriodIndex = timeline.getIndexOfPeriod(periodUidAndPosition.first);
     }
     internalPlayer.seekTo(timeline, windowIndex, C.msToUs(positionMs));
-    for (Player.EventListener listener : listeners) {
+    notifyListeners(listener -> listener.onPositionDiscontinuity(DISCONTINUITY_REASON_SEEK));
-      listener.onPositionDiscontinuity(DISCONTINUITY_REASON_SEEK);
-    }
   }
 
   @Override
@@ -594,17 +588,13 @@ import java.util.concurrent.CopyOnWriteArraySet;
         PlaybackParameters playbackParameters = (PlaybackParameters) msg.obj;
         if (!this.playbackParameters.equals(playbackParameters)) {
           this.playbackParameters = playbackParameters;
-          for (Player.EventListener listener : listeners) {
+          notifyListeners(listener -> listener.onPlaybackParametersChanged(playbackParameters));
-            listener.onPlaybackParametersChanged(playbackParameters);
-          }
         }
         break;
       case ExoPlayerImplInternal.MSG_ERROR:
         ExoPlaybackException playbackError = (ExoPlaybackException) msg.obj;
         this.playbackError = playbackError;
-        for (Player.EventListener listener : listeners) {
+        notifyListeners(listener -> listener.onPlayerError(playbackError));
-          listener.onPlayerError(playbackError);
-        }
         break;
       default:
         throw new IllegalStateException();
@@ -703,6 +693,15 @@ import java.util.concurrent.CopyOnWriteArraySet;
             playWhenReady));
   }
 
+  private void notifyListeners(ListenerInvocation listenerInvocation) {
+    notifyListeners(
+        () -> {
+          for (Player.EventListener listener : listeners) {
+            listenerInvocation.invokeListener(listener);
+          }
+        });
+  }
+
   private void notifyListeners(Runnable listenerNotificationRunnable) {
     boolean isRunningRecursiveListenerNotification = !pendingListenerNotifications.isEmpty();
     pendingListenerNotifications.addLast(listenerNotificationRunnable);
@@ -806,24 +805,8 @@ import java.util.concurrent.CopyOnWriteArraySet;
     }
   }
 
-  private static final class PlayWhenReadyUpdate implements Runnable {
+  private interface ListenerInvocation {
 
-    private final Set<Player.EventListener> listeners;
+    void invokeListener(Player.EventListener listener);
-    private final boolean playWhenReady;
-    private final int playbackState;
-
-    public PlayWhenReadyUpdate(
-        Set<Player.EventListener> listeners, boolean playWhenReady, int playbackState) {
-      this.listeners = listeners;
-      this.playWhenReady = playWhenReady;
-      this.playbackState = playbackState;
-    }
-
-    @Override
-    public void run() {
-      for (Player.EventListener listener : listeners) {
-        listener.onPlayerStateChanged(playWhenReady, playbackState);
-      }
-    }
   }
 }

library/core/src/test/java/com/google/android/exoplayer2/ExoPlayerTest.java

@@ -498,12 +498,12 @@ public final class ExoPlayerTest {
             .waitForPlaybackState(Player.STATE_READY)
             .seek(10)
             // Start playback and wait until playback reaches second window.
-            .play()
+            .playUntilStartOfWindow(/* windowIndex= */ 1)
-            .waitForPositionDiscontinuity()
             // Seek twice in concession, expecting the first seek to be replaced (and thus except
             // only on seek processed callback).
             .seek(5)
             .seek(60)
+            .play()
             .build();
     final List<Integer> playbackStatesWhenSeekProcessed = new ArrayList<>();
     EventListener eventListener =
@@ -2058,8 +2058,11 @@ public final class ExoPlayerTest {
             .pause()
             .waitForPlaybackState(Player.STATE_READY)
             .seek(/* windowIndex= */ 0, /* positionMs= */ 9999)
+            .waitForSeekProcessed()
             .seek(/* windowIndex= */ 0, /* positionMs= */ 1)
+            .waitForSeekProcessed()
             .seek(/* windowIndex= */ 0, /* positionMs= */ 9999)
+            .waitForSeekProcessed()
             .play()
             .build();
     ExoPlayerTestRunner testRunner =