[Fetch API] Put body members directly on Response/Request

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 handleNullBody(event) {
   event.respondWith(new Response(null));
 }
 
 function handleReject(event) {
   event.respondWith(new Promise(function(resolve, reject) {
       reject('rejected!');
     }));
 }
 
 function handleFetch(event) {
   event.respondWith(fetch('other.html'));
 }
 
 function handleFormPost(event) {
   event.respondWith(new Promise(function(resolve) {
-      event.request.body.asText()
+      event.request.text()
         .then(function(result) {
             resolve(new Response(event.request.method + ':' + result));
           })
     }));
 }
 
 var logForMultipleRespondWith = '';
 
 function handleMultipleRespondWith(event) {
   for (var i = 0; i < 3; ++i) {
@@ skipping 28 matching lines @@
       }
     }
 
     if (handler) {
       handler.fn(event);
     } else {
       event.respondWith(new Response(new Blob(
         ['Service Worker got an unexpected request: ' + url])));
     }
   });