private Map<String, String> addDefaultHeaders(Map<String, String> headers) {
    Map<String, String> newHeaders = new HashMap<>(headers);
    for (Entry<String, String> entry : defaultHeaders.entrySet()) {
      if (!newHeaders.containsKey(entry.getKey())) {
        newHeaders.put(entry.getKey(), entry.getValue());
      }
    }
    return newHeaders;
  }
Shut down this GeoApiContext instance, reclaiming resources. After shutdown() has been called,
no further queries may be done against this instance.
src/main/java/com/google/maps/GeoApiContext.java