Use protocol relative URL for OSM tiles

src/objectliterals.jsdoc

@@ -697,7 +697,7 @@
  *     function to load a tile given a URL.
  * @property {string|undefined} url URL template. Must include `{x}`, `{y}`,
  *     and `{z}` placeholders. Default is
- *     `http://{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png`.
+ *     `//{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png`.
  * @todo stability experimental
  */
 

src/ol/source/osmsource.js

@@ -26,7 +26,7 @@ ol.source.OSM = function(opt_options) {
       options.crossOrigin : 'anonymous';
 
   var url = goog.isDef(options.url) ?
-      options.url : 'http://{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png';
+      options.url : '//{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png';
 
   goog.base(this, {
     attributions: attributions,