Moving maxZoom default to XYZ source.

No reason this convenience should be restricted to the OSM layer.

src/objectliterals.jsdoc

@@ -613,7 +613,8 @@
  * @property {ol.Extent|undefined} extent Extent.
  * @property {string|undefined} logo Logo.
  * @property {ol.ProjectionLike} projection Projection.
- * @property {number} maxZoom Max zoom.
+ * @property {number|undefined} maxZoom Optional max zoom level.  The default is
+ *     18.
  * @property {number|undefined} minZoom Unsupported (TODO: remove this).
  * @property {ol.TileUrlFunctionType|undefined} tileUrlFunction Optional
  *     function to get tile URL given a tile coordinate and the projection.

src/ol/source/osmsource.js

@@ -23,8 +23,6 @@ ol.source.OSM = function(opt_options) {
     attributions = ol.source.OSM.ATTRIBUTIONS;
   }
 
-  var maxZoom = goog.isDef(options.maxZoom) ? options.maxZoom : 18;
-
   var url = goog.isDef(options.url) ?
       options.url : 'http://{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png';
 
@@ -32,7 +30,7 @@ ol.source.OSM = function(opt_options) {
     attributions: attributions,
     crossOrigin: 'anonymous',
     opaque: true,
-    maxZoom: maxZoom,
+    maxZoom: options.maxZoom,
     url: url
   });
 

src/ol/source/xyzsource.js

@@ -33,8 +33,10 @@ ol.source.XYZ = function(options) {
         ol.TileUrlFunction.expandUrl(options.url));
   }
 
+  var maxZoom = goog.isDef(options.maxZoom) ? options.maxZoom : 18;
+
   var tileGrid = new ol.tilegrid.XYZ({
-    maxZoom: options.maxZoom
+    maxZoom: maxZoom
   });
 
   var tileCoordTransform = tileGrid.createTileCoordTransform({