Extarct setCacheChannelHeader middleware from controller's context

lib/cartodb/controllers/named_maps.js

@@ -56,7 +56,7 @@ NamedMapsController.prototype.register = function(app) {
         getAffectedTables(),
         getTile(tileOptions),
         this.setSurrogateKey(),
-        this.setCacheChannelHeader(),
+        setCacheChannelHeader(),
         this.setLastModifiedHeader(),
         this.setCacheControlHeader(),
         this.setContentTypeHeader(),
@@ -85,7 +85,7 @@ NamedMapsController.prototype.register = function(app) {
         getImage(staticOptions),
         incrementMapViews({ metadataBackend: this.metadataBackend }),
         this.setSurrogateKey(),
-        this.setCacheChannelHeader(),
+        setCacheChannelHeader(),
         this.setLastModifiedHeader(),
         this.setCacheControlHeader(),
         this.setContentTypeHeader(),
@@ -419,7 +419,7 @@ function templateBounds(view) {
     return false;
 }
 
-NamedMapsController.prototype.setCacheChannelHeader = function () {
+function setCacheChannelHeader () {
     return function setCacheChannelHeaderMiddleware (req, res, next) {
         const { affectedTablesAndLastUpdate } = res.locals;
 
@@ -429,7 +429,7 @@ NamedMapsController.prototype.setCacheChannelHeader = function () {
 
         next();
     };
-};
+}
 
 NamedMapsController.prototype.setSurrogateKey = function () {
     return function setSurrogateKeyMiddleware(req, res, next) {