The method mentioned in this answer: https://stackoverflow.com/a/19818178/194642 does not seem to work anymore. How does one use web component's element in angular.dart component?
@Component(
selector: "custom-elem",
template: "<div id='container-elem'> <content></content></div>")
class CustomElem extends ShadowRootAware{
  onShadowRoot(_) {
    //do something
  }
}
Now, I would expect the following html fragment:
<custom-elem> 
  <span>Sample content</span>
</custom-elem> 
to result in following within #shadow-root:
<div id='container-elem'>
  <content> 
    <span>Sample content</span>
  </content>
</div>