Layer hierarchy for renderers.

src/ol/layer/Layer.js

@@ -0,0 +1,7 @@
+goog.provide('ol.layer.Layer');
+
+/**
+ * @constructor
+ * @export
+ */
+ol.layer.Layer = function() {};

src/ol/layer/TileLayer.js

@@ -0,0 +1,11 @@
+goog.provide('ol.layer.TileLayer');
+
+goog.require('ol.layer.Layer');
+
+/**
+ * @constructor
+ * @extends {ol.layer.Layer}
+ */
+ol.layer.TileLayer = function() {};
+
+goog.inherits(ol.layer.TileLayer, ol.layer.Layer);

src/ol/layer/XYZ.js

@@ -1,13 +1,16 @@
 goog.provide('ol.layer.XYZ');
 
+goog.require('ol.layer.TileLayer');
 goog.require('ol.Projection');
 goog.require('ol.Tile');
 goog.require('ol.TileSet');
 
 /**
  * Class for XYZ layers.
+ *
  * @export
  * @constructor
+ * @extends {ol.layer.TileLayer}
  * @param {string} url URL template. E.g.
  *     http://a.tile.openstreetmap.org/{z}/{x}/{y}.png.
  */
@@ -66,6 +69,8 @@ ol.layer.XYZ = function(url) {
 
 };
 
+goog.inherits(ol.layer.XYZ, ol.layer.TileLayer);
+
 /**
  * Set tile width and height.
  * @param {number} width