title: shadow dom - know when dom is rendered/changed
body: <p>I am writing a chrome extension that modifies elements properties as a page is loaded or changes.</p>
  
  <p>I do this using a Mutation Observer. However the observer's handler is not called when shadow-dom (ie, embedded twitter posts) are loaded/changed.</p>
  
  <p>Is there a way to get an event when shadow-dom is loaded/changes or to hook a mutation observer to it ? </p>
  
  <p>Thanks!</p>