Exposing BaseMediaChunkOutput as public so that BaseMediaChunk.init() is unit testable.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=198062017

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

@@ -15,16 +15,16 @@
  */
 package com.google.android.exoplayer2.source.chunk;
 
+import android.support.annotation.VisibleForTesting;
 import android.util.Log;
 import com.google.android.exoplayer2.extractor.DummyTrackOutput;
 import com.google.android.exoplayer2.extractor.TrackOutput;
 import com.google.android.exoplayer2.source.SampleQueue;
 import com.google.android.exoplayer2.source.chunk.ChunkExtractorWrapper.TrackOutputProvider;
 
-/**
- * An output for {@link BaseMediaChunk}s.
- */
-/* package */ final class BaseMediaChunkOutput implements TrackOutputProvider {
+/** An output for {@link BaseMediaChunk}s. */
+@VisibleForTesting(otherwise = VisibleForTesting.PACKAGE_PRIVATE)
+public final class BaseMediaChunkOutput implements TrackOutputProvider {
 
   private static final String TAG = "BaseMediaChunkOutput";