releaseRequest_(request) {
    this.requests_.remove(request.getId());
    if (request.getImageLoader()) {
      this.releaseObject_(request.getToken());
      request.getImageLoader().dispose();
    }
    request.fireImageEventCallback();
  }
Finishes processing of a request and releases its token if possible.
@param {ee.MapTileManager.Request_} request The object to process.
@private