handleAvailableToken_(request, token) {
    if (request.getImageLoader() || request.getAborted()) {
      this.releaseObject_(token);
      return;
    }

    // Associate the request with the token.
    request.setToken(token);
    token.setActive(true);

    // Add an ImageLoader object to the request.
    // TODO(user): consider using goog.labs.net.image, which is simpler.
    request.setImageLoader(new goog.net.ImageLoader());

    // Send the request.
    if (!request.retry()) {
      throw Error('Cannot dispatch first request!');
    }
  }
Handles a Token object that became available. Sets up the callback,
and starts the process to send the request.
@param {ee.MapTileManager.Request_} request A request to associate
    the token with.
@param {ee.MapTileManager.Token_} token The available Token_ object.
@private