Add layout tests to check Accept request header values observed by Service Worker

third_party/WebKit/LayoutTests/http/tests/serviceworker/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(
     ['Referrer: ' + event.request.referrer])));
 }
 
+function handleAccept(event) {
+  event.respondWith(new Response(new Blob(
+    ['Accept: ' + event.request.headers.get('accept')])));
+}
+
 function handleClientId(event) {
   var body;
   if (event.clientId !== null) {
     body = 'Client ID Found: ' + event.clientId;
   } else {
     body = 'Client ID Not Found';
   }
   event.respondWith(new Response(body));
 }
 
@@ skipping 45 matching lines @@
         'bodyUsed: ' + lastResponseForUsedCheck.bodyUsed));
   }
 }
 
 self.addEventListener('fetch', function(event) {
     var url = event.request.url;
     var handlers = [
       { pattern: '?string', fn: handleString },
       { pattern: '?blob', fn: handleBlob },
       { pattern: '?referrer', fn: handleReferrer },
+      { pattern: '?accept', fn: handleAccept },
       { 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 }
     ];
 
     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])));
     }
   });