Extract incrementMapViews middleware from controllers middleware

lib/cartodb/controllers/named_maps.js

@@ -83,7 +83,7 @@ NamedMapsController.prototype.register = function(app) {
         prepareLayerFilterFromPreviewLayers(staticOptions),
         getStaticImageOptions({ tablesExtentApi: this.tablesExtentApi }),
         getImage(staticOptions),
-        this.incrementMapViews(),
+        incrementMapViews({ metadataBackend: this.metadataBackend }),
         this.setSurrogateKey(),
         this.setCacheChannelHeader(),
         this.setLastModifiedHeader(),
@@ -366,7 +366,7 @@ function incrementMapViewsError (ctx) {
     return `ERROR: failed to increment mapview count for user '${ctx.user}': ${ctx.err}`;
 }
 
-NamedMapsController.prototype.incrementMapViews = function () {
+function incrementMapViews ({ metadataBackend }) {
     return function incrementMapViewsMiddleware(req, res, next) {
         const { user, namedMapProvider } = res.locals;
 
@@ -378,7 +378,7 @@ NamedMapsController.prototype.incrementMapViews = function () {
 
             const statTag = mapConfig.obj().stat_tag;
 
-            this.metadataBackend.incMapviewCount(user, statTag, (err) => {
+            metadataBackend.incMapviewCount(user, statTag, (err) => {
                 if (err) {
                     global.logger.log(incrementMapViewsError({ user, err }));
                 }
@@ -386,8 +386,8 @@ NamedMapsController.prototype.incrementMapViews = function () {
                 next();
             });
         });
-    }.bind(this);
-};
+    };
+}
 
 function templateZoomCenter(view) {
     if (view.zoom !== undefined && view.center) {