_replaceMatchesPseudo(selector, matches) {
    const parts = selector.split(MATCHES_REPLACEMENT);
    return matches.reduce((acc, cur, idx) => acc + cur + parts[idx + 1], parts[0]);
  }
Replace MATCHES_REPLACMENT character with the given set of `:matches()`
selectors.

@param {string} selector
@param {!Array<string>} matches
@return {string}