Call goog.getUid in ol.Object constructor

src/ol/object.js

@@ -48,6 +48,12 @@ ol.ObjectEventType = {
 ol.ObjectEvent = function(type, key) {
   goog.base(this, type);
 
+  // Call goog.getUid to ensure that the order of objects' ids is the same as
+  // the order in which they were created.  This also helps to ensure that
+  // object properties are always added in the same order, which helps many
+  // JavaScript engines generate faster code.
+  goog.getUid(this);
+
   /**
    * The name of the property whose value is changing.
    * @type {string}