void showDuration(long startNs) {
    if (mDurationCallback != null) {
      mDurationCallback.showDuration(startNs);
    }
  }
Simple extension of {@link BasePostprocessor} for this sample app that allows to pass along the
runtime of the post-processing.
samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/postprocessor/BasePostprocessorWithDurationCallback.java