Add setter method to child data holder of abstract concatenated timeline.

Prevents that we forget to set variables.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=159939180

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

@@ -28,7 +28,7 @@ import com.google.android.exoplayer2.Timeline;
   /**
   /**
    * Meta data of a child timeline.
    * Meta data of a child timeline.
    */
    */
-  protected static class ChildDataHolder {
+  protected static final class ChildDataHolder {
 
 
     /**
     /**
      * Child timeline.
      * Child timeline.
@@ -50,6 +50,22 @@ import com.google.android.exoplayer2.Timeline;
      */
      */
     public Object uid;
     public Object uid;
 
 
+    /**
+     * Set child holder data.
+     *
+     * @param timeline Child timeline.
+     * @param firstPeriodIndexInChild First period index belonging to the child timeline.
+     * @param firstWindowIndexInChild First window index belonging to the child timeline.
+     * @param uid UID of child timeline.
+     */
+    public void setData(Timeline timeline, int firstPeriodIndexInChild, int firstWindowIndexInChild,
+        Object uid) {
+      this.timeline = timeline;
+      this.firstPeriodIndexInChild = firstPeriodIndexInChild;
+      this.firstWindowIndexInChild = firstWindowIndexInChild;
+      this.uid = uid;
+    }
+
   }
   }
 
 
   private final ChildDataHolder childDataHolder;
   private final ChildDataHolder childDataHolder;

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

@@ -231,10 +231,8 @@ public final class ConcatenatingMediaSource implements MediaSource {
     }
     }
 
 
     private void getChildDataByChildIndex(int childIndex, ChildDataHolder childData) {
     private void getChildDataByChildIndex(int childIndex, ChildDataHolder childData) {
-      childData.timeline = timelines[childIndex];
-      childData.firstPeriodIndexInChild = getFirstPeriodIndexInChild(childIndex);
-      childData.firstWindowIndexInChild = getFirstWindowIndexInChild(childIndex);
-      childData.uid = childIndex;
+      childData.setData(timelines[childIndex], getFirstPeriodIndexInChild(childIndex),
+          getFirstWindowIndexInChild(childIndex), childIndex);
     }
     }
 
 
     private int getChildIndexByPeriodIndex(int periodIndex) {
     private int getChildIndexByPeriodIndex(int periodIndex) {

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

@@ -141,10 +141,8 @@ public final class LoopingMediaSource implements MediaSource {
     }
     }
 
 
     private void getChildDataByChildIndex(int childIndex, ChildDataHolder childData) {
     private void getChildDataByChildIndex(int childIndex, ChildDataHolder childData) {
-      childData.timeline = childTimeline;
-      childData.firstPeriodIndexInChild = childIndex * childPeriodCount;
-      childData.firstWindowIndexInChild = childIndex * childWindowCount;
-      childData.uid = childIndex;
+      childData.setData(childTimeline, childIndex * childPeriodCount, childIndex * childWindowCount,
+          childIndex);
     }
     }
 
 
   }
   }