code: function (obj, prop) {
                  shared.utils.dassert(getTracker(obj) === this);
                  if(obj.hasOwnProperty(prop)) {
                      var value = obj[prop];
                      if(delete obj[prop]) {
                          wrapProp(obj, prop, value);
                      } else {
                          throw new Error('Unwrappable property found: ' + prop);
                      }
                  }
              }
docs: Wrap a property for get/set tracking