option `hitCallback` doesn't work for google analytics.

I'm trying to track outbound link navigations, and found that the way to do this with google analytics is to send an event and in the options set a `hitCallback` key to a function that will be called when the event has been received. This just flat out doesn't seem to work.. here's my component.js:

``` js
function exitToMessenger() {
console.log('redirecting to messenger.com!!')
window.location.href = 'https://www.messenger.com/t/heyimlea';
}

export default Ember.Component.extend({
metrics: Ember.inject.service(),
actions: {
sendToMessenger() {
console.log('send to messenger called')
var metrics = Ember.get(this, 'metrics')

var eventData = {
hitType: 'event',
eventCategory: 'Outbound Link',
eventAction: 'click',
eventLabel: 'Sent to messenger!',
eventValue: 'https://www.messenger.com/t/heyimlea'
};

// if (navigator.sendBeacon) {
// //https://github.com/googleanalytics/autotrack/blob/bcdd409c22430553a2a43275386877bf37600e68/lib/plugins/outbound-form-tracker.js#L77
// //https://developer.mozilla.org/en-US/docs/Web/API/Navigator/sendBeacon
// eventData.transport = 'beacon'
// metrics.trackEvent(eventData)
// //metrics.trackPage({page: '/sent2messenger', title: "exiting to messenger" });
// //be sure analytics.js calls sendBeacon before exiting
// setTimeout(exitToMessenger, 4)
// } else {
eventData.hitCallback = exitToMessenger;
metrics.trackEvent(eventData)
// }
}
}
```

Searching something along the lines of 'analytics track outbound link' I find this help article from google analytics suggesting this method: https://support.google.com/analytics/answer/1136920?hl=en
Here's the docs on hitCallback: https://developers.google.com/analytics/devguides/collection/analyticsjs/sending-hits#hitcallback

I'd love to get this fixed and tested asap so that the ember community can have one comprehensive addon for analytics

Start with component.js and the metrics.trackEvent call, then trace how eventData options reach the Google Analytics integration. Compare hitCallback handling with the linked Google Analytics documentation and add a regression test that confirms the callback is invoked for the outbound event.

Written by the indexing model from the issue text.