Import w3c tests for the service workers

third_party/WebKit/LayoutTests/imported/wpt/service-workers/service-worker/resources/events-worker.js

 var eventsSeen = [];
 
 function handler(event) { eventsSeen.push(event.type); }
 
 ['activate', 'install'].forEach(function(type) {
     self.addEventListener(type, handler);
   });
 
 onmessage = function(e) {
   var message = e.data;
   message.port.postMessage({events: eventsSeen});
 };