@Override
  public CacheKey getPostprocessorCacheKey() {
    return new SimpleCacheKey(
        String.format((Locale) null, "text=%s,count=%d", mWatermarkText, mCount));
  }
Adds a watermark at random positions to the bitmap like {@link WatermarkPostprocessor}. However,
this implementation specifies a cache key such that the bitmap stays the same every time the
postprocessor is applied.
samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/postprocessor/CachedWatermarkPostprocessor.java