Make TrackSelection implement equals/hashCode.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=116638211

library/src/main/java/com/google/android/exoplayer/FrameworkSampleSource.java

@@ -169,8 +169,8 @@ public final class FrameworkSampleSource implements SampleSource {
   @Override
   public TrackStream enable(TrackSelection selection, long positionUs) {
     Assertions.checkState(prepared);
-    Assertions.checkState(selection.tracks.length == 1);
+    Assertions.checkState(selection.length == 1);
-    Assertions.checkState(selection.tracks[0] == 0);
+    Assertions.checkState(selection.getTrack(0) == 0);
     int track = selection.group;
     Assertions.checkState(trackStates[track] == TRACK_STATE_DISABLED);
     enabledTrackCount++;

library/src/main/java/com/google/android/exoplayer/MultiSampleSource.java

@@ -80,7 +80,7 @@ public class MultiSampleSource implements SampleSource {
   public TrackStream enable(TrackSelection selection, long positionUs) {
     Pair<Integer, Integer> sourceAndGroup = getSourceAndTrackGroupIndices(selection.group);
     return sources[sourceAndGroup.first].enable(
-        new TrackSelection(sourceAndGroup.second, selection.tracks), positionUs);
+        new TrackSelection(sourceAndGroup.second, selection.getTracks()), positionUs);
   }
 
   @Override

library/src/main/java/com/google/android/exoplayer/TrackSelection.java

@@ -15,27 +15,80 @@
  */
 package com.google.android.exoplayer;
 
+import com.google.android.exoplayer.util.Assertions;
+
+import java.util.Arrays;
+
 /**
  * Defines a track selection.
  */
 public final class TrackSelection {
 
   /**
-   * The index of the {@link TrackGroup}.
+   * The index of the selected {@link TrackGroup}.
    */
   public final int group;
   /**
-   * The indices of the individual tracks within the {@link TrackGroup}.
+   * The number of selected tracks within the {@link TrackGroup}. Always greater than zero.
    */
-  public final int[] tracks;
+  public final int length;
+
+  private final int[] tracks;
+
+  // Lazily initialized hashcode.
+  private int hashCode;
 
   /**
    * @param group The index of the {@link TrackGroup}.
-   * @param tracks The indices of the individual tracks within the {@link TrackGroup}.
+   * @param tracks The indices of the selected tracks within the {@link TrackGroup}. Must not be
+   *     null or empty.
    */
   public TrackSelection(int group, int... tracks) {
+    Assertions.checkState(tracks.length > 0);
     this.group = group;
     this.tracks = tracks;
+    this.length = tracks.length;
+  }
+
+  /**
+   * Gets the index of the selected track at a given index in the selection.
+   *
+   * @param index The index in the selection.
+   * @return The index of the selected track.
+   */
+  public int getTrack(int index) {
+    return getTracks()[index];
+  }
+
+  /**
+   * Gets a copy of the individual track indices.
+   *
+   * @return The track indices.
+   */
+  public int[] getTracks() {
+    return tracks.clone();
+  }
+
+  @Override
+  public int hashCode() {
+    if (hashCode == 0) {
+      int result = 17;
+      result = 31 * result + group;
+      result = 31 * result + Arrays.hashCode(tracks);
+    }
+    return hashCode;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+    if (obj == null || getClass() != obj.getClass()) {
+      return false;
+    }
+    TrackSelection other = (TrackSelection) obj;
+    return group == other.group && Arrays.equals(tracks, other.tracks);
   }
 
 }

library/src/main/java/com/google/android/exoplayer/chunk/ChunkSampleSource.java

@@ -188,7 +188,7 @@ public class ChunkSampleSource implements SampleSource, TrackStream, Loader.Call
     Assertions.checkState(state == STATE_PREPARED);
     Assertions.checkState(enabledTrackCount++ == 0);
     state = STATE_ENABLED;
-    chunkSource.enable(selection.tracks);
+    chunkSource.enable(selection.getTracks());
     loadControl.register(this, bufferSizeContribution);
     downstreamFormat = null;
     downstreamSampleFormat = null;

library/src/main/java/com/google/android/exoplayer/extractor/ExtractorSampleSource.java

@@ -299,8 +299,8 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
   @Override
   public TrackStream enable(TrackSelection selection, long positionUs) {
     Assertions.checkState(prepared);
-    Assertions.checkState(selection.tracks.length == 1);
+    Assertions.checkState(selection.length == 1);
-    Assertions.checkState(selection.tracks[0] == 0);
+    Assertions.checkState(selection.getTrack(0) == 0);
     int track = selection.group;
     Assertions.checkState(!trackEnabledStates[track]);
     enabledTrackCount++;

library/src/main/java/com/google/android/exoplayer/hls/HlsSampleSource.java

@@ -191,7 +191,7 @@ public final class HlsSampleSource implements SampleSource, Loader.Callback {
   public TrackStream enable(TrackSelection selection, long positionUs) {
     Assertions.checkState(prepared);
     int group = selection.group;
-    int[] tracks = selection.tracks;
+    int[] tracks = selection.getTracks();
     setTrackGroupEnabledState(group, true);
     downstreamSampleFormats[group] = null;
     pendingResets[group] = false;