Use ol.inherits instead of goog.inherits

src/ol/source/stamensource.js

@@ -101,7 +101,7 @@ ol.source.Stamen = function(options) {
       'https://stamen-tiles-{a-d}.a.ssl.fastly.net/' + options.layer +
       '/{z}/{x}/{y}.' + layerConfig.extension;
 
-  goog.base(this, {
+  ol.source.XYZ.call(this, {
     attributions: ol.source.Stamen.ATTRIBUTIONS,
     cacheSize: options.cacheSize,
     crossOrigin: 'anonymous',
@@ -114,7 +114,7 @@ ol.source.Stamen = function(options) {
   });
 
 };
-goog.inherits(ol.source.Stamen, ol.source.XYZ);
+ol.inherits(ol.source.Stamen, ol.source.XYZ);
 
 
 /**