Allow custom properties in the constructor using the properties option

src/ol/layer/BaseTile.js

@@ -32,6 +32,7 @@ import {assign} from '../obj.js';
  * temporary layers. The standard way to add a layer to a map and have it managed by the map is to
  * use {@link module:ol/Map#addLayer}.
  * @property {boolean} [useInterimTilesOnError=true] Use interim tiles on error.
+ * @property {Object<string, *>} [properties] Arbitrary observable properties. Can be accessed with `#get()` and `#set()`.
  */
 
 /**