i'm playing with it, and angular doesn't seem to like injecting filters into filters. You could try:

```javascript
angular.module("Prometheus.services").factory('sharedHostnameBehavior', function() {
  return function(input) {
    var a = document.createElement("a");
    a.href = input;
    return a.host;
  }
});
```
And work off of the return from this function?