title: increase Service Worker life time
body: <p>I'm trying push notifications using service workers.
  use my own server to send notifications and eventSource is used to establish the connection. 
  after i open the webpage service worker is running perfectly. but it stops after few seconds.
  what i want is to run service worker without getting stopped. i want it to run until the browser is opened. can anyone recommend a way to do that. ? </p>
  
  <p>this is my ServiceWorker JS</p>
  
  <pre><code>/**
   * 
   */
  'use strict';
  var eventSource2 = new EventSource("Servlet");
  console.log('Started', eventSource2);
  eventSource2.addEventListener('install', function(event) {
      eventSource2.skipWaiting();
      console.log('Installed', event);
  
  });
  
  eventSource2.addEventListener('push',function(event) {
                      console.log(event.data);
                      var title = event.data;
                      self.registration.showNotification(title,{
                                          'body' : event.data,
                                          'icon' : 'http://icons.iconarchive.com/icons/designbolts/free-multimedia/1024/iMac-icon.png',
                                          'tag' : 'click',
                                      });
                      console.log("data from down", event.data);
                  });
  
  eventSource2.addEventListener('activate', function(event){
      console.log('Activated', event);
  });
  
  eventSource2.addEventListener('fetch', function(event) {
      console.log('Push message', event);
  });
  </code></pre>