connectAndWaitForPeer() {
    this.channel_.connect();
    // Set a listener for when the peer exists.
    return new Promise(
        /** @suppress {visibility} suppression added to enable type checking */
        (res) => this.channel_.peerWindowDeferred_.addCallback(res));
  }
Begin, but don't finish, connection to a peer.

@return {!Promise<undefined>} A timing hook for the unstable period between
    the creation of the peer and the connection notification from that
peer.