No-op cleanup of DashTimeline

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=204451894

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

@@ -1083,10 +1083,9 @@ public final class DashMediaSource extends BaseMediaSource {
 
     @Override
     public Period getPeriod(int periodIndex, Period period, boolean setIdentifiers) {
-      Assertions.checkIndex(periodIndex, 0, manifest.getPeriodCount());
+      Assertions.checkIndex(periodIndex, 0, getPeriodCount());
       Object id = setIdentifiers ? manifest.getPeriod(periodIndex).id : null;
-      Object uid = setIdentifiers ? firstPeriodId
-          + Assertions.checkIndex(periodIndex, 0, manifest.getPeriodCount()) : null;
+      Object uid = setIdentifiers ? (firstPeriodId + periodIndex) : null;
       return period.set(id, uid, 0, manifest.getPeriodDurationUs(periodIndex),
           C.msToUs(manifest.getPeriod(periodIndex).startMs - manifest.getPeriod(0).startMs)
               - offsetInFirstPeriodUs);
@@ -1113,7 +1112,7 @@ public final class DashMediaSource extends BaseMediaSource {
           windowDefaultStartPositionUs,
           windowDurationUs,
           /* firstPeriodIndex= */ 0,
-          manifest.getPeriodCount() - 1,
+          /* lastPeriodIndex= */ getPeriodCount() - 1,
           offsetInFirstPeriodUs);
     }
 
@@ -1123,8 +1122,8 @@ public final class DashMediaSource extends BaseMediaSource {
         return C.INDEX_UNSET;
       }
       int periodId = (int) uid;
-      return periodId < firstPeriodId || periodId >= firstPeriodId + getPeriodCount()
-          ? C.INDEX_UNSET : (periodId - firstPeriodId);
+      int periodIndex = periodId - firstPeriodId;
+      return periodIndex < 0 || periodIndex >= getPeriodCount() ? C.INDEX_UNSET : periodIndex;
     }
 
     private long getAdjustedWindowDefaultStartPositionUs(long defaultPositionProjectionUs) {