code: @Override
      synchronized protected void onHostAnchor(GVRAnchor anchor, CloudAnchorCallback cb) {
          Anchor newAnchor = mSession.hostCloudAnchor(((ARCoreAnchor) anchor).getAnchorAR());
          pendingAnchors.put(newAnchor, cb);
      }
docs: This method hosts an anchor. The {@code listener} will be invoked when the results are
  available.