A bit late but I got something similar that I'm busy building and here is the code to get current location - be sure to use local server to test.
Include relevant scripts from CDN:
    <script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&signed_in=true&callback=initMap">
HTML
<div id="map"></div>
CSS
html, body {
    height: 100%;
    margin: 0;
    padding: 0;
}
#map {
    height: 100%;
}
JS
var map = new google.maps.Map(document.getElementById('map'), {
    center: {lat: -34.397, lng: 150.644},
    zoom: 6
});
var infoWindow = new google.maps.InfoWindow({map: map});
// Try HTML5 geolocation.
if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(function(position) {
        var pos = {
            lat: position.coords.latitude,
            lng: position.coords.longitude
        };
        infoWindow.setPosition(pos);
        infoWindow.setContent('Location found.');
        map.setCenter(pos);
    }, function() {
        handleLocationError(true, infoWindow, map.getCenter());
    });
} else {
    // Browser doesn't support Geolocation
    handleLocationError(false, infoWindow, map.getCenter());
}
function handleLocationError(browserHasGeolocation, infoWindow, pos) {
    infoWindow.setPosition(pos);
    infoWindow.setContent(browserHasGeolocation ?
                          'Error: The Geolocation service failed.' :
                          'Error: Your browser doesn\'t support geolocation.');
}
DEMO
https://jsfiddle.net/ToreanJoel/4ythpy02/