Properly release sample streams for DASH

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132301223

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

@@ -626,12 +626,12 @@ import java.io.IOException;
       }
     }
     enabledRenderers = new Renderer[0];
+    releasePeriodHoldersFrom(playingPeriodHolder != null ? playingPeriodHolder
+        : loadingPeriodHolder);
     if (mediaSource != null) {
       mediaSource.releaseSource();
       mediaSource = null;
     }
-    releasePeriodHoldersFrom(playingPeriodHolder != null ? playingPeriodHolder
-        : loadingPeriodHolder);
     isTimelineReady = false;
     isTimelineEnded = false;
     playingPeriodHolder = null;

library/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaPeriod.java

@@ -91,6 +91,12 @@ import java.util.List;
     }
   }
 
+  public void release() {
+    for (ChunkSampleStream<DashChunkSource> sampleStream : sampleStreams) {
+      sampleStream.release();
+    }
+  }
+
   @Override
   public void maybeThrowPrepareError() throws IOException {
     manifestLoaderErrorThrower.maybeThrowError();

library/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java

@@ -182,7 +182,9 @@ public final class DashMediaSource implements MediaSource {
 
   @Override
   public void releasePeriod(MediaPeriod mediaPeriod) {
-    periodsById.remove(((DashMediaPeriod) mediaPeriod).id);
+    DashMediaPeriod dashMediaPeriod = (DashMediaPeriod) mediaPeriod;
+    dashMediaPeriod.release();
+    periodsById.remove(dashMediaPeriod.id);
   }
 
   @Override