如何检测何时关闭操作弹出窗口?

http://crbug.com/31262#c13

var timeoutId = 0;
function popupPing() {
    if(timeoutId != 0) {
        clearTimeout(timeoutId);
    }

    timeoutId = setTimeout(function() {
        popupClosed();
        timeoutId = 0;
    }, 1000);
}

function popupClosed() {
    //...
}

ping();
function ping() {
    chrome.extension.getBackgroundPage().popupPing();
    setTimeout(ping, 500);
}