Refactor ArrayList fields to List

Author: imericxu

app/src/main/java/org/schabi/newpipe/player/playqueue/PlayQueue.java

@@ -41,12 +41,12 @@
 public abstract class PlayQueue implements Serializable {
     public static final boolean DEBUG = MainActivity.DEBUG;
 
-    private ArrayList<PlayQueueItem> backup;
-    private ArrayList<PlayQueueItem> streams;
+    private List<PlayQueueItem> backup;
+    private List<PlayQueueItem> streams;
 
     @NonNull
     private final AtomicInteger queueIndex;
-    private final ArrayList<PlayQueueItem> history;
+    private final List<PlayQueueItem> history;
 
     private transient BehaviorSubject<PlayQueueEvent> eventBroadcast;
     private transient Flowable<PlayQueueEvent> broadcastReceiver;