If you need to use Google’s tiles in LeafletJS, you can follow the same URL structure as OpenStreetMap. The tile servers are mt0 .. mt3, and the XYZ are specified a little differently. Here you go:
L.tileLayer('http://{s}.google.com/vt/x={x}&y={y}&z={z}', { subdomains : ['mt0','mt1','mt2','mt3'], attribution: 'Tiles Courtesy of <a href="http://maps.google.com" target="_blank">Google</a>', maxZoom: 18 }).addTo(map);