Make DefaultLoadErrorHandlingPolicy non-final

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=214584874

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultLoadErrorHandlingPolicy.java

@@ -22,7 +22,7 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 
 /** Default implementation of {@link LoadErrorHandlingPolicy}. */
-public final class DefaultLoadErrorHandlingPolicy implements LoadErrorHandlingPolicy {
+public class DefaultLoadErrorHandlingPolicy implements LoadErrorHandlingPolicy {
 
   /** The default minimum number of times to retry loading data prior to propagating the error. */
   public static final int DEFAULT_MIN_LOADABLE_RETRY_COUNT = 3;