Fix seeking with repeated periods

newPlayingPeriodHolder could be set then updated if seeking to a repeated period
that was loaded more than once. This led to MediaPeriodHolders leaking.

Only set newPlayingPeriodHolder once so that any later holders with the same
period identifier get released.

Also add a regression test. FakeMediaSource checks that all created
MediaPeriods were released when it is released.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=172591937

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

@@ -261,6 +261,22 @@ public final class ExoPlayerTest extends TestCase {
     assertTrue(renderer.isEnded);
   }
 
+  public void testPeriodHoldersReleasedAfterSeekWithRepeatModeAll() throws Exception {
+    Timeline fakeTimeline = new FakeTimeline(new TimelineWindowDefinition(true, false, 100000));
+    FakeRenderer renderer = new FakeRenderer(Builder.VIDEO_FORMAT);
+    ActionSchedule actionSchedule = new ActionSchedule.Builder("testPeriodHoldersReleased")
+        .setRepeatMode(Player.REPEAT_MODE_ALL)
+        .waitForPositionDiscontinuity()
+        .seek(0) // Seek with repeat mode set to REPEAT_MODE_ALL.
+        .waitForPositionDiscontinuity()
+        .setRepeatMode(Player.REPEAT_MODE_OFF) // Turn off repeat so that playback can finish.
+        .build();
+    new ExoPlayerTestRunner.Builder()
+        .setTimeline(fakeTimeline).setRenderers(renderer).setActionSchedule(actionSchedule)
+        .build().start().blockUntilEnded(TIMEOUT_MS);
+    assertTrue(renderer.isEnded);
+  }
+
   public void testSeekProcessedCallback() throws Exception {
     Timeline timeline = new FakeTimeline(
         new TimelineWindowDefinition(true, false, 100000),

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

@@ -753,7 +753,8 @@ import java.io.IOException;
       // Clear the timeline, but keep the requested period if it is already prepared.
       MediaPeriodHolder periodHolder = playingPeriodHolder;
       while (periodHolder != null) {
-        if (shouldKeepPeriodHolder(periodId, periodPositionUs, periodHolder)) {
+        if (newPlayingPeriodHolder == null
+            && shouldKeepPeriodHolder(periodId, periodPositionUs, periodHolder)) {
           newPlayingPeriodHolder = periodHolder;
         } else {
           periodHolder.release();

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeMediaSource.java

@@ -116,4 +116,5 @@ public class FakeMediaSource implements MediaSource {
     }
     return new TrackGroupArray(trackGroups);
   }
+
 }