Avoid track group array error-prone reference quality check in CastPlayer.

Also replaced the duplicated EMPTY track group array with the one already defined
in TrackGroupArray.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=175670266

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

@@ -86,7 +86,6 @@ public final class CastPlayer implements Player {
   private static final int RENDERER_INDEX_AUDIO = 1;
   private static final int RENDERER_INDEX_AUDIO = 1;
   private static final int RENDERER_INDEX_TEXT = 2;
   private static final int RENDERER_INDEX_TEXT = 2;
   private static final long PROGRESS_REPORT_PERIOD_MS = 1000;
   private static final long PROGRESS_REPORT_PERIOD_MS = 1000;
-  private static final TrackGroupArray EMPTY_TRACK_GROUP_ARRAY = new TrackGroupArray();
   private static final TrackSelectionArray EMPTY_TRACK_SELECTION_ARRAY =
   private static final TrackSelectionArray EMPTY_TRACK_SELECTION_ARRAY =
       new TrackSelectionArray(null, null, null);
       new TrackSelectionArray(null, null, null);
   private static final long[] EMPTY_TRACK_ID_ARRAY = new long[0];
   private static final long[] EMPTY_TRACK_ID_ARRAY = new long[0];
@@ -137,7 +136,7 @@ public final class CastPlayer implements Player {
     playbackState = STATE_IDLE;
     playbackState = STATE_IDLE;
     repeatMode = REPEAT_MODE_OFF;
     repeatMode = REPEAT_MODE_OFF;
     currentTimeline = CastTimeline.EMPTY_CAST_TIMELINE;
     currentTimeline = CastTimeline.EMPTY_CAST_TIMELINE;
-    currentTrackGroups = EMPTY_TRACK_GROUP_ARRAY;
+    currentTrackGroups = TrackGroupArray.EMPTY;
     currentTrackSelection = EMPTY_TRACK_SELECTION_ARRAY;
     currentTrackSelection = EMPTY_TRACK_SELECTION_ARRAY;
     pendingSeekWindowIndex = C.INDEX_UNSET;
     pendingSeekWindowIndex = C.INDEX_UNSET;
     pendingSeekPositionMs = C.TIME_UNSET;
     pendingSeekPositionMs = C.TIME_UNSET;
@@ -596,8 +595,8 @@ public final class CastPlayer implements Player {
     MediaInfo mediaInfo = mediaStatus != null ? mediaStatus.getMediaInfo() : null;
     MediaInfo mediaInfo = mediaStatus != null ? mediaStatus.getMediaInfo() : null;
     List<MediaTrack> castMediaTracks = mediaInfo != null ? mediaInfo.getMediaTracks() : null;
     List<MediaTrack> castMediaTracks = mediaInfo != null ? mediaInfo.getMediaTracks() : null;
     if (castMediaTracks == null || castMediaTracks.isEmpty()) {
     if (castMediaTracks == null || castMediaTracks.isEmpty()) {
-      boolean hasChanged = currentTrackGroups != EMPTY_TRACK_GROUP_ARRAY;
-      currentTrackGroups = EMPTY_TRACK_GROUP_ARRAY;
+      boolean hasChanged = !currentTrackGroups.isEmpty();
+      currentTrackGroups = TrackGroupArray.EMPTY;
       currentTrackSelection = EMPTY_TRACK_SELECTION_ARRAY;
       currentTrackSelection = EMPTY_TRACK_SELECTION_ARRAY;
       return hasChanged;
       return hasChanged;
     }
     }

library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java

@@ -62,8 +62,11 @@ public final class TrackGroupArray {
    * @param group The group.
    * @param group The group.
    * @return The index of the group, or {@link C#INDEX_UNSET} if no such group exists.
    * @return The index of the group, or {@link C#INDEX_UNSET} if no such group exists.
    */
    */
+  @SuppressWarnings("ReferenceEquality")
   public int indexOf(TrackGroup group) {
   public int indexOf(TrackGroup group) {
     for (int i = 0; i < length; i++) {
     for (int i = 0; i < length; i++) {
+      // Suppressed reference equality warning because this is looking for the index of a specific
+      // TrackGroup object, not the index of a potential equal TrackGroup.
       if (trackGroups[i] == group) {
       if (trackGroups[i] == group) {
         return i;
         return i;
       }
       }
@@ -71,6 +74,13 @@ public final class TrackGroupArray {
     return C.INDEX_UNSET;
     return C.INDEX_UNSET;
   }
   }
 
 
+  /**
+   * Returns whether this track group array is empty.
+   */
+  public boolean isEmpty() {
+    return length == 0;
+  }
+
   @Override
   @Override
   public int hashCode() {
   public int hashCode() {
     if (hashCode == 0) {
     if (hashCode == 0) {