tracker = function(e) {
      var retargettedEvent = Object.create(e, {
        'target': {
          'value': self,
          'writable': false
        },
        'type': {
          'value': e.type,
          'writable': false
        }
      });
      self['dispatchEvent'](retargettedEvent);
    }
Active flow, if any.
@type {wtf.trace.Flow}
@private