Angular-google-maps: Property controls is not available on NativeMap object

Issue description
I am inserting a searchbox on the map to search for addresses as you can see on this tutorial at (Google Maps API doc)[https://developers.google.com/maps/documentation/javascript/examples/places-searchbox].

In order to to that, I got the NativeMap and push the input element into the map using something like this:

this.gmaps.getNativeMap().then(map => {
      let input = document.getElementById('my-search-box');
      let searchBox = new google.maps.places.SearchBox(input);
      map.controls[google.maps.ControlPosition.TOP_LEFT].push(input);
      searchBox.addListener('places_changed', () => this.placesChanged(searchBox));
    });

As the controls is not mapped on the object returned from map I always get the error message:
Property 'controls' does not exist on type 'GoogleMap'.

but it works anyway.

As the controls property allows us to do cool stuff once we got the nativeMap, I think implement it could be nice for future releases.

angular2 & angular2-google-maps version
angular2 - 2.0.0-rc.6
angular2-google-maps 0.14.0