Upstream service worker `fetch` tests to WPT

third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/resources/fetch-event-test-worker.js

 function handleString(event) {
   event.respondWith(new Response('Test string'));
 }
 
 function handleBlob(event) {
   event.respondWith(new Response(new Blob(['Test blob'])));
 }
 
 function handleReferrer(event) {
   event.respondWith(new Response(new Blob(
@@ skipping 95 matching lines @@
   event.respondWith(new Response(body, {
       headers: { 'Content-Type': 'text/event-stream' }
     }
   ));
 }
 
 function handleIntegrity(event) {
   event.respondWith(new Response(event.request.integrity));
 }
 
+function handleHeaders(event) {
+  const headers = Array.from(event.request.headers);
+  event.respondWith(new Response(JSON.stringify(headers)));
+}
+
 self.addEventListener('fetch', function(event) {
     var url = event.request.url;
     var handlers = [
       { pattern: '?string', fn: handleString },
       { pattern: '?blob', fn: handleBlob },
       { pattern: '?referrerFull', fn: handleReferrerFull },
       { pattern: '?referrerPolicy', fn: handleReferrerPolicy },
       { pattern: '?referrer', fn: handleReferrer },
       { pattern: '?clientId', fn: handleClientId },
       { pattern: '?ignore', fn: function() {} },
       { pattern: '?null', fn: handleNullBody },
       { pattern: '?fetch', fn: handleFetch },
       { pattern: '?form-post', fn: handleFormPost },
       { pattern: '?multiple-respond-with', fn: handleMultipleRespondWith },
       { pattern: '?used-check', fn: handleUsedCheck },
       { pattern: '?fragment-check', fn: handleFragmentCheck },
       { pattern: '?cache', fn: handleCache },
       { pattern: '?eventsource', fn: handleEventSource },
       { pattern: '?integrity', fn: handleIntegrity },
+      { pattern: '?headers', fn: handleHeaders },
     ];
 
     var handler = null;
     for (var i = 0; i < handlers.length; ++i) {
       if (url.indexOf(handlers[i].pattern) != -1) {
         handler = handlers[i];
         break;
       }
     }
 
     if (handler) {
       handler.fn(event);
     } else {
       event.respondWith(new Response(new Blob(
         ['Service Worker got an unexpected request: ' + url])));
     }
   });