Make setConstantBitrateSeekingEnabled consistent with other method

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=210093143

library/core/src/main/java/com/google/android/exoplayer2/extractor/DefaultExtractorsFactory.java

@@ -95,9 +95,12 @@ public final class DefaultExtractorsFactory implements ExtractorsFactory {
    *
    * @param constantBitrateSeekingEnabled Whether approximate seeking using a constant bitrate
    *     assumption should be enabled for all extractors that support it.
+   * @return The factory, for convenience.
    */
-  public void setConstantBitrateSeekingEnabled(boolean constantBitrateSeekingEnabled) {
+  public synchronized DefaultExtractorsFactory setConstantBitrateSeekingEnabled(
+      boolean constantBitrateSeekingEnabled) {
     this.constantBitrateSeekingEnabled = constantBitrateSeekingEnabled;
+    return this;
   }
 
   /**