Replace goog.getUid with ol.getUid

src/ol/ol.js

@@ -265,6 +265,28 @@ ol.inherits = function(childCtor, parentCtor) {
 ol.nullFunction = function() {};
 
 
+/**
+ * Gets a unique ID for an object. This mutates the object so that further calls
+ * with the same object as a parameter returns the same value. Adapted from
+ * goog.getUid.
+ *
+ * @param {Object} obj The object to get the unique ID for.
+ * @return {number} The unique ID for the object.
+ */
+ol.getUid = function(obj) {
+  return obj.ol_uid ||
+      (obj.ol_uid = ++ol.uidCounter_);
+};
+
+
+/**
+ * Counter for getUid.
+ * @type {number}
+ * @private
+ */
+ol.uidCounter_ = 0;
+
+
 /**
  * @see https://github.com/tc39/proposal-global
  */