A Fluid userscript to show the unread message count for a Google Inbox SSB.

inbox.newMessageCount.js

/**
 * A userscript for Fluid. This script updates the dock badge for a Google Inbox
 * SSB to the number of unread messages in the current view. Note that the user
 * must be navigated to the Inbox, and it will only count unread messages
 * that are currently displayed on the screen.
 */

initialization();

function initialization() {
    updateUnreadBadge();
}

function getUnreadCount() {
    // if we aren't on the inbox we don't know the current unread count
    if (location.pathname != '/' || location.hash !== '') {
        return '?';
    }
    // we are on the inbox, so get the count
    var els = document.getElementsByClassName('ss');
    return (els.length) ? els.length : '';
}

function updateUnreadBadge() {
    window.fluid.dockBadge = getUnreadCount();
    setTimeout(updateUnreadBadge, 1000);
}