Fix Google map loading issue.

Also use Leaflet class hook for google api loading.

Fixes #565

public/js/lib/leaflet/extends/L.Google.js

@@ -4,15 +4,17 @@
  */
 
 // Google layer plugin wrapper. Loads Google Maps library with API key included.
-define(['Params', 'leaflet', 'leaflet-plugins/lru', 'leaflet-plugins/Leaflet.GoogleMutant'], function (P, L) {
+define(['Params', 'leaflet', 'leaflet-plugins/lru', 'leaflet-plugins/Leaflet.GoogleMutant'], function (P, L, lru) {
     const keyParam = P.settings.publicApiKeys.googleMaps.length ? '&key=' + P.settings.publicApiKeys.googleMaps : '';
     const url = 'https://maps.googleapis.com/maps/api/js?v=weekly&region=RU' + keyParam;
 
     // Load Google Maps API library asynchronously.
-    require(['async!' + url]);
-
+    L.GridLayer.GoogleMutant.addInitHook(function() {
+        require(['async!' + url]);
+    });
     return function (options) {
         options = options || {};
+        options.lru = new lru.LRUMap(100); // Tile LRU cache.
 
         return new L.GridLayer.GoogleMutant(options);
     };

public/js/lib/leaflet/plugins/Leaflet.GoogleMutant.js

@@ -11,8 +11,7 @@ this stuff is worth it, you can buy me a beer in return.
 */
 
 //import { LRUMap } from "./lru_map.js";
-// We have to use requirejs to load module, ES6 syntax won't work here.
-const { LRUMap } = require('leaflet-plugins/lru');
+// LRU is passed in options.
 
 function waitForAPI(callback, context) {
 	let checkCounter = 0,
@@ -47,7 +46,7 @@ L.GridLayer.GoogleMutant = L.GridLayer.extend({
 
 		// Couple data structures indexed by tile key
 		this._tileCallbacks = {}; // Callbacks for promises for tiles that are expected
-		this._lru = new LRUMap(100); // Tile LRU cache
+		this._lru = options.lru; // Tile LRU cache
 
 		this._imagesPerTile = this.options.type === "hybrid" ? 2 : 1;