used, applying this mixin will cause Polymer to skip dirty checking for
   * objects and arrays (always consider them to be "dirty").  This allows a
   * user to make a deep modification to a bound object graph, and then either
   * simply re-set the object (e.g. `this.items = this.items`) or call `notifyPath`
   * (e.g. `this.notifyPath('items')`) to update the tree.  Note that all
   * elements that wish to be updated based on deep mutations must apply this
   * mixin or otherwise skip strict dirty checki