I decided against consistency in `ol.Object` because I don't think `ol.Object.getListeners` is necessary.  My assumption was that the [enumeration was used](https://github.com/openlayers/ol3/commit/331ee15ac8235aea0e69374ee4a759a7a7d0f8af) in an attempt to avoid clashes with user-set property names (before `ol.Object` got [a dedicated storage object](https://github.com/openlayers/ol3/commit/d6ff58305de50954fd68506f3cde4c411c0f72ac)).

I think we could safely remove the `ol.ObjectProperty` enumeration altogether (saving a few bytes as a result).  But that's a separate issue.