Called by the DOM when this element has been removed from the live document.
More information can be found in the Custom Elements draft specification.
Source
/**
* Called by the DOM when this element has been removed from the live
* document.
*
* More information can be found in the
* [Custom Elements](http://w3c.github.io/webcomponents/spec/custom/#dfn-detached-callback)
* draft specification.
*/
@Experimental()
void detached() {
// For the deprecation period, call the old callback.
leftView();
}