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