function onClickDirective(){
        return {
            restrict: 'A',
            scope: false,
            require: 'googleChart',
            link: function(scope, element, attrs, googleChartController){
                callback.$inject = ['args', 'chart', 'chartWrapper'];
                function callback(args, chart, chartWrapper){
                    scope.$apply(function (){
                        scope.$eval(attrs.agcOnClick, {args: args, chart: chart, chartWrapper: chartWrapper});
                    });
                }
                googleChartController.registerChartListener('click', callback, this);
            }
        };
    }
Forces angular-google-chart to load this object as the google library.
 Makes no checks to ensure that the object passed is compatible. Use
 at own risk.