[ServiceWorker] Add support of FetchEvent's request.body.

LayoutTests/http/tests/serviceworker/resources/fetch-event-test-worker.js

 function handleString(event) {
-    event.respondWith(new Response('Test string'));
+  event.respondWith(new Response('Test string'));
 }
 
 function handleBlob(event) {
-    event.respondWith(new Response(new Blob(['Test blob'])));
+  event.respondWith(new Response(new Blob(['Test blob'])));
 }
 
 function handleReferrer(event) {
-    event.respondWith(new Response(new Blob(['Referrer: ' + event.request.referrer])));
+  event.respondWith(new Response(new Blob(
+    ['Referrer: ' + event.request.referrer])));
 }
 
 function handleNullBody(event) {
-    event.respondWith(new Response(null));
+  event.respondWith(new Response(null));
 }
 
 function handleReject(event) {
-    event.respondWith(new Promise(function(resolve, reject) {
-        reject('rejected!');
+  event.respondWith(new Promise(function(resolve, reject) {
+      reject('rejected!');
     }));
 }
 
 function handleFetch(event) {
-    event.respondWith(fetch('other.html'));
+  event.respondWith(fetch('other.html'));
+}
+
+function handleFormPost(event) {
+  event.respondWith(new Promise(function(resolve) {
+      event.request.body.asText()
+        .then(function(result) {
+            resolve(new Response(event.request.method + ':' + result));
+          })
+    }));
 }
 
 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: '?ignore', fn: function() {} },
-        { pattern: '?null', fn: handleNullBody },
-        { pattern: '?reject', fn: handleReject },
-        { pattern: '?fetch', fn: handleFetch }
+      { pattern: '?string', fn: handleString },
+      { pattern: '?blob', fn: handleBlob },
+      { pattern: '?referrer', fn: handleReferrer },
+      { pattern: '?ignore', fn: function() {} },
+      { pattern: '?null', fn: handleNullBody },
+      { pattern: '?reject', fn: handleReject },
+      { pattern: '?fetch', fn: handleFetch },
+      { pattern: '?form-post', fn: handleFormPost }
     ];
 
     var handler = null;
     for (var i = 0; i < handlers.length; ++i) {
-       if (url.indexOf(handlers[i].pattern) != -1) {
-           handler = handlers[i];
-           break;
-       }
+      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])));
-});
+    if (handler) {
+      handler.fn(event);
+    } else {
+      event.respondWith(new Response(new Blob(
+        ['Service Worker got an unexpected request: ' + url])));
+    }
+  });