docs: private boolean hasHashChanged(Hasher hasher, RegData regDatum) {
          String urlExternalForm = regDatum.getURLExternalForm();
          Boolean modified = mUrlExternalForm2Modified.get(urlExternalForm);
          if (modified != null) {
              return modified;
          }
          // Check hash
          String newHash = hasher.hashURL(urlExternalForm);
          modified = !newHash.equals(regDatum.getHash());
          mUrlExternalForm2Modified.put(urlExternalForm, modified);
          return modified;
      }