add an ol.layer.xyz factory

src/api/layer/xyz.js

@@ -0,0 +1,29 @@
+goog.provide('ol.layer.xyz');
+
+/**
+ * @export
+ * @param {Object} opt_arg Config object.
+ * @return {ol.layer.XYZ}
+ */
+ol.layer.xyz = function(opt_arg) {
+    if (opt_arg instanceof ol.layer.XYZ) {
+        return opt_arg;
+    }
+
+    /** @type {string} */
+    var url;
+
+    var usage = 'ol.layer.xyz accepts an object with a "url" property';
+
+    if (goog.isObject(opt_arg)) {
+        url = opt_arg['url'];
+    } else {
+        throw new Error(usage);
+    }
+
+    if (!goog.isDef(url)) {
+        throw new Error(usage);
+    }
+
+    return new ol.layer.XYZ(url);
+};

src/ol.js

@@ -5,6 +5,7 @@ goog.require('ol.event.Events');
 goog.require("ol.map");
 goog.require("ol.loc");
 goog.require("ol.projection");
+goog.require("ol.layer.xyz");
 goog.require("ol.Tile");
 goog.require("ol.TileSet");
 goog.require("ol.geom.geometry");

test/index.html

@@ -52,6 +52,7 @@
   <script type="text/javascript" src="spec/api/loc.test.js"></script>
   <script type="text/javascript" src="spec/api/map.test.js"></script>
   <script type="text/javascript" src="spec/api/projection.test.js"></script>
+  <script type="text/javascript" src="spec/api/layer/xyz.test.js"></script>
   <script type="text/javascript" src="spec/ol/Events.test.js"></script>
   <script type="text/javascript" src="spec/ol/Projection.test.js"></script>
   <script type="text/javascript" src="spec/ol/Tile.test.js"></script>

test/spec/api/layer/xyz.test.js

@@ -0,0 +1,17 @@
+describe('ol.layer.xyz', function() {
+
+    it("doesn't allow empty construction", function() {
+
+        expect(function() {
+            // nowhere
+            var layer = ol.layer.xyz();
+        }).toThrow();
+
+    });
+
+    it("creates an ol.layer.XYZ instance", function() {
+        var layer = ol.layer.xyz({url: 'http://foo/{x}/{y}/{z}'});
+        expect(layer).toBeA(ol.layer.XYZ);
+    });
+
+});