From http://stackoverflow.com/questions/668286/detect-blocked-popup-in-chrome

check_popup_blocked.js

function checkPopupBlocked(poppedWindow) {
 setTimeout(function(){doCheckPopupBlocked(poppedWindow);}, 5000);
}

function doCheckPopupBlocked(poppedWindow) {

    var result = false;

    try {
        if (typeof poppedWindow == 'undefined') {
            // Safari with popup blocker... leaves the popup window handle undefined
            result = true;
        }
        else if (poppedWindow && poppedWindow.closed) {
            // This happens if the user opens and closes the client window...
            // Confusing because the handle is still available, but it's in a "closed" state.
            // We're not saying that the window is not being blocked, we're just saying
            // that the window has been closed before the test could be run.
            result = false;
        }
        else if (poppedWindow && poppedWindow.outerWidth == 0) {
            // This is usually Chrome's doing. The outerWidth (and most other size/location info)
         // will be left at 0, EVEN THOUGH the contents of the popup will exist (including the
         // test function we check for next). The outerWidth starts as 0, so a sufficient delay
         // after attempting to pop is needed.
            result = true;
        }
        else if (poppedWindow && poppedWindow.test) {
            // This is the actual test. The client window should be fine.
            result = false;
        }
        else {
            // Else we'll assume the window is not OK
            result = true;
        }

    } catch (err) {
        //if (console) {
        //    console.warn("Could not access popup window", err);
        //}
    }

    if(result)
     alert("The popup was blocked. You must allow popups to use this site.");
}

Usage:

var popup=window.open('location',etc...);
checkPopupBlocked(popup);