code: public static Key[] globalKeysOfClass(final Class clz) {
      return KeySnapshot.globalSnapshot().filter(new KeySnapshot.KVFilter() {
        @Override public boolean filter(KeySnapshot.KeyInfo k) { return Value.isSubclassOf(k._type, clz); }
      }).keys();
    }
docs: Return all the keys of the given class.
  @param clz Class
  @return array of keys in this snapshot with the given class