title: Get Firebase Web Notification Even Close Chrome
body: <p>I am currently working on a video web application. We rely on notification to notify provider there is call in. </p>
  
  <p>Firebase works well even when I close the tab. I found that if there is any chrome's thread running in background, I will get notification. </p>
  
  <p>Is there any way that I can make a background thread active even the user click close button on chrome? how about chrome extension? does it approach the goal? </p>