I would add an onclick handler on 'chart_div' that would open the requested window.
Add the line below after chart.draw(data, options);
$("#chart_div").on("click", OpenNewWindow());
Then add this method after the google function.
function OpenNewWindow() {
window.open('https://www.bing.com', '', 'width=800,left=' + ((screen.width / 2) - 400) + ',top=' + ((screen.height / 2) - 300) + ',height=600,status=yes,scrollbars=yes');
}
Note you will need jQuery for this solution.
http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.11.0.min.js