Define CueGroup.EMPTY_TIME_ZERO for convenience

We create an empty CueGroup in many places as default or
where none is needed. Instead, we can define a constant
for this purpose and reuse it.

PiperOrigin-RevId: 467944841
(cherry picked from commit 29208ec1)

extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/CastPlayer.java

@@ -111,8 +111,6 @@ public final class CastPlayer extends BasePlayer {
 
   private static final long PROGRESS_REPORT_PERIOD_MS = 1000;
   private static final long[] EMPTY_TRACK_ID_ARRAY = new long[0];
-  private static final CueGroup EMPTY_CUE_GROUP =
-      new CueGroup(ImmutableList.of(), /* presentationTimeUs= */ 0);
 
   private final CastContext castContext;
   private final MediaItemConverter mediaItemConverter;
@@ -726,7 +724,7 @@ public final class CastPlayer extends BasePlayer {
   /** This method is not supported and returns an empty {@link CueGroup}. */
   @Override
   public CueGroup getCurrentCues() {
-    return EMPTY_CUE_GROUP;
+    return CueGroup.EMPTY_TIME_ZERO;
   }
 
   /** This method is not supported and always returns {@link DeviceInfo#UNKNOWN}. */

library/common/src/main/java/com/google/android/exoplayer2/text/CueGroup.java

@@ -34,6 +34,11 @@ import java.util.List;
 
 /** Class to represent the state of active {@link Cue Cues} at a particular time. */
 public final class CueGroup implements Bundleable {
+
+  /** An empty group with no {@link Cue Cues} and presentation time of zero. */
+  public static final CueGroup EMPTY_TIME_ZERO =
+      new CueGroup(ImmutableList.of(), /* presentationTimeUs= */ 0);
+
   /**
    * The cues in this group.
    *

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

@@ -345,7 +345,7 @@ import java.util.concurrent.TimeoutException;
       } else {
         audioSessionId = Util.generateAudioSessionIdV21(applicationContext);
       }
-      currentCueGroup = new CueGroup(ImmutableList.of(), /* presentationTimeUs= */ 0);
+      currentCueGroup = CueGroup.EMPTY_TIME_ZERO;
       throwsWhenUsingWrongThread = true;
 
       addListener(analyticsCollector);
@@ -990,7 +990,7 @@ import java.util.concurrent.TimeoutException;
       checkNotNull(priorityTaskManager).remove(C.PRIORITY_PLAYBACK);
       isPriorityTaskManagerRegistered = false;
     }
-    currentCueGroup = new CueGroup(ImmutableList.of(), /* presentationTimeUs= */ 0);
+    currentCueGroup = CueGroup.EMPTY_TIME_ZERO;
     playerReleased = true;
   }