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/structs/priorityqueue.js

@@ -56,7 +56,8 @@ ol.structs.PriorityQueue = function(priorityFunction, keyFunction) {
 
 
 /**
- * @const {number}
+ * @const
+ * @type {number}
  */
 ol.structs.PriorityQueue.DROP = Infinity;