code: private void getResPathKeys(String[] keys, int depth) {
          ICUResourceBundle b = this;
          while (depth > 0) {
              keys[--depth] = b.key;
              b = b.container;
              assert (depth == 0) == (b.container == null);
          }
      }
docs: Fills some of the keys array with the keys on the path to this resource object.
  Writes the top-level key into index 0 and increments from there.
  
  @param keys
  @param depth must be {@link #getResDepth()}