title: How to add shadow to a GMSMarker?
body: <p>I'm trying to add some <strong>shadow</strong> to the markers on my GMSMapView but configuring the shadow properties of GMSMarkerLayer does not appear to have any effect. </p>
  
  <pre><code>GMSMarker *marker = [[GMSMarker alloc] init];
  [marker setMap:self.mapView];
  marker.snippet = @"Description";
  marker.title = @"Title";
  marker.position = busData.location.coordinate;
  marker.icon = [UIImage imageNamed:@"BusMarker"];
  marker.layer.shadowOpacity = 0.7;
  marker.layer.shadowOffset = CGSizeMake(0, 3);
  marker.layer.shadowRadius = 5.0;
  marker.layer.shadowColor = [UIColor blackColor].CGColor;
  </code></pre>
  
  <p>I'm setting the same properties I'd use on a CALayer object, as GMSMarkerLayer subclasses CALayer.</p>
  
  <p>Am I doing something wrong or is this a bug? I'm using SDK version 1.10.0.</p>