Extract getNamedMapProvider middleware from controller's context

lib/cartodb/controllers/named_maps.js

@@ -42,6 +42,7 @@ module.exports = NamedMapsController;
 
 NamedMapsController.prototype.register = function(app) {
     const tileOptions = {
+        namedMapProviderCache: this.namedMapProviderCache,
         label: 'NAMED_MAP_TILE'
     };
 
@@ -50,7 +51,7 @@ NamedMapsController.prototype.register = function(app) {
         cors(),
         userMiddleware(),
         this.prepareContext,
-        this.getNamedMapProvider(tileOptions),
+        getNamedMapProvider(tileOptions),
         this.getAffectedTables(),
         this.getTile(tileOptions),
         this.setSurrogateKey(),
@@ -63,6 +64,7 @@ NamedMapsController.prototype.register = function(app) {
     );
 
     const staticOptions = {
+        namedMapProviderCache: this.namedMapProviderCache,
         forcedFormat: 'png',
         label: 'STATIC_VIZ_MAP'
     };
@@ -73,7 +75,7 @@ NamedMapsController.prototype.register = function(app) {
         userMiddleware(),
         allowQueryParams(['layer', 'zoom', 'lon', 'lat', 'bbox']),
         this.prepareContext,
-        this.getNamedMapProvider(staticOptions),
+        getNamedMapProvider(staticOptions),
         this.getAffectedTables(),
         this.getTemplate(staticOptions),
         this.prepareLayerFilterFromPreviewLayers(staticOptions),
@@ -89,7 +91,7 @@ NamedMapsController.prototype.register = function(app) {
     );
 };
 
-NamedMapsController.prototype.getNamedMapProvider = function ({ label, forcedFormat = null }) {
+function getNamedMapProvider ({ namedMapProviderCache, label, forcedFormat = null }) {
     return function getNamedMapProviderMiddleware (req, res, next) {
         const { user } = res.locals;
         const { config, auth_token } = req.query;
@@ -102,7 +104,7 @@ NamedMapsController.prototype.getNamedMapProvider = function ({ label, forcedFor
 
         const params = getRequestParams(res.locals);
 
-        this.namedMapProviderCache.get(user, template_id, config, auth_token, params, (err, namedMapProvider) => {
+        namedMapProviderCache.get(user, template_id, config, auth_token, params, (err, namedMapProvider) => {
             if (err) {
                 err.label = label;
                 return next(err);
@@ -112,7 +114,7 @@ NamedMapsController.prototype.getNamedMapProvider = function ({ label, forcedFor
 
             next();
         });
-    }.bind(this);
+    };
 };
 
 NamedMapsController.prototype.getAffectedTables = function () {