Create 'type' annotation for 'const' variables

From https://developers.google.com/closure/compiler/docs/js-for-compiler:
  "The type declaration and additional comment are optional. If you
  provide a type declaration, put the declaration on a separate line."

src/ol/css.js

@@ -4,7 +4,8 @@ goog.provide('ol.css');
 /**
  * The CSS class that we'll give the DOM elements to have them unselectable.
  *
- * @const {string}
+ * @const
+ * @type {string}
  */
 ol.css.CLASS_UNSELECTABLE = 'ol-unselectable';
 
@@ -12,6 +13,7 @@ ol.css.CLASS_UNSELECTABLE = 'ol-unselectable';
 /**
  * The CSS class for unsupported feature.
  *
- * @const {string}
+ * @const
+ * @type {string}
  */
 ol.css.CLASS_UNSUPPORTED = 'ol-unsupported';