@Nullable
  @Override
  public CacheKey getPostprocessorCacheKey() {
    if (mCacheKey == null) {
      final String key = String.format((Locale) null, "i%dr%d", mIterations, mBlurRadius);
      mCacheKey = new SimpleCacheKey(key);
    }
    return mCacheKey;
  }
A fast and memory-efficient post processor performing an iterative box blur. For details see
{@link NativeBlurFilter#iterativeBoxBlur(Bitmap, int, int)}.
native-filters/src/main/java/com/facebook/imagepipeline/postprocessors/IterativeBoxBlurPostProcessor.java