Use assertInstanceof instead of getTileSource

src/ol/layer/tilelayer.js

@@ -1,7 +1,6 @@
 goog.provide('ol.layer.Tile');
 
 goog.require('ol.layer.Layer');
-goog.require('ol.source.Tile');
 
 
 /**
@@ -44,14 +43,6 @@ goog.exportProperty(
     ol.layer.Tile.prototype.getPreload);
 
 
-/**
- * @return {ol.source.Tile} Source.
- */
-ol.layer.Tile.prototype.getTileSource = function() {
-  return /** @type {ol.source.Tile} */ (this.getSource());
-};
-
-
 /**
  * @param {number} preload Preload.
  * @todo stability experimental