code: function (res, cfg) {
                  var providerInstance = providerInstances[cfg.provider];
                  providerInstance.load({
                      fn : this._retrieveMapInstance,
                      scope : this,
                      args : cfg
                  });
              }
docs: Load the provider dependencies. Called after loading the provider class
  @param {Object} res
  @param {aria.map.CfgBeans:CreateMapCfg} cfg
  @private