var message = new gcm.Message({
    collapseKey: "demo",
    delayWhileIdle: true,
    timeToLive: 3,
    data: {
        test: 'value'
    }
});

var sender = new gcm.Sender(config.gcmKey);

var tokens = [];

... (to add tokens) ...

sender.send(message, tokens, 3, function (err, res) { ... }

self.addEventListener('push', function(event) {
    console.log('Push message', event);
    var title = 'Push message';
    event.waitUntil(
        self.registration.showNotification(title, {
            body: 'Test',
            icon: 'img/icon.png',
        }));
});