Set ol.layer.Tile#getSource return type to ol.source.Tile

externs/olx.js

@@ -2838,7 +2838,7 @@ olx.layer.ImageOptions.prototype.maxResolution;
  *     opacity: (number|undefined),
  *     preload: (number|undefined),
  *     saturation: (number|undefined),
- *     source: ol.source.Source,
+ *     source: ol.source.Tile,
  *     visible: (boolean|undefined),
  *     extent: (ol.Extent|undefined),
  *     minResolution: (number|undefined),
@@ -2900,7 +2900,7 @@ olx.layer.TileOptions.prototype.saturation;
 
 /**
  * Source for this layer.
- * @type {ol.source.Source}
+ * @type {ol.source.Tile}
  * @api stable
  */
 olx.layer.TileOptions.prototype.source;

src/ol/layer/tilelayer.js

@@ -28,8 +28,7 @@ ol.layer.TileProperty = {
  * @api stable
  */
 ol.layer.Tile = function(options) {
-  goog.base(this, options);
-
+  goog.base(this,  /** @type {olx.layer.LayerOptions} */ (options));
 };
 goog.inherits(ol.layer.Tile, ol.layer.Layer);
 
@@ -49,6 +48,14 @@ goog.exportProperty(
     ol.layer.Tile.prototype.getPreload);
 
 
+/**
+ * @function
+ * @return {ol.source.Tile} Source.
+ * @api stable
+ */
+ol.layer.Tile.prototype.getSource;
+
+
 /**
  * @param {number} preload The level to preload tiles up to.
  * @observable