Use assertInstanceof instead of getVectorSource

src/ol/layer/vectorlayer.js

@@ -2,7 +2,6 @@ goog.provide('ol.layer.Vector');
 
 goog.require('ol.feature');
 goog.require('ol.layer.Layer');
-goog.require('ol.source.Vector');
 
 
 /**
@@ -63,14 +62,6 @@ goog.exportProperty(
     ol.layer.Vector.prototype.getStyleFunction);
 
 
-/**
- * @return {ol.source.Source} Vector source.
- */
-ol.layer.Vector.prototype.getVectorSource = function() {
-  return /** @type {ol.source.Vector} */ (this.getSource());
-};
-
-
 /**
  * @param {function(ol.geom.Geometry): boolean|undefined} renderGeometryFunction
  *     Render geometry function.