(function() {
    var docViewerURL = "https://docs.google.com/viewer?url=";
    var docLinkXpath = "//a[contains(@href,'facdn')]";
    var iterator = document.evaluate(docLinkXpath, document, null, XPathResult.UNORDERED_NODE_ITERATOR_TYPE, null);

    var link = iterator.iterateNext();
    var links = [];

    // Can't modify while iterating over xpath results, transfer to array first
    while (link) {
        links.push(link);
        link = iterator.iterateNext();
    }

    for (var i=0; i < links.length; i++) {
        var link = links[i];
        var viewLink = document.createElement('a');
        viewLink.href = docViewerURL + link.href;
        viewLink.innerHTML = ' [View] ';
        viewLink.target = '_blank';

        link.parentElement.insertBefore(viewLink, link.nextSibling);
    }
})();