[Fetch] Body consume function should not set bodyUsed flag.

LayoutTests/http/tests/cachestorage/script-tests/cache-add.js

 if (self.importScripts) {
     importScripts('/resources/testharness.js');
     importScripts('/resources/testharness-helpers.js');
     importScripts('../resources/test-helpers.js');
 }
 
 cache_test(function(cache) {
     return assert_promise_rejects(
       cache.add(),
       new TypeError(),
@@ skipping 21 matching lines @@
       .then(function(result) {
           assert_equals(result, undefined,
                         'Cache.add should resolve with undefined on success.');
         });
   }, 'Cache.add called with Request object');
 
 cache_test(function(cache) {
     var request = new Request('../resources/simple.txt', {method: 'POST', body: 'Hello'});
     return request.text()
       .then(function() {
-          assert_true(request.bodyUsed);
+          assert_false(request.bodyUsed);
         })
       .then(function() {
-          return assert_promise_rejects(
-            cache.add(request),
-            new TypeError(),
-            'Cache.add with a Request object with a used body should reject ' +
-            'with a TypeError.');
+          return cache.add(request);
         });
   }, 'Cache.add called with Request object with a used body');
 
 cache_test(function(cache) {
     var request = new Request('../resources/simple.txt', {method: 'POST', body: 'Hello'});
     return cache.add(request)
       .then(function(result) {
           assert_equals(result, undefined,
                         'Cache.add should resolve with undefined on success.');
         })
@@ skipping 80 matching lines @@
 cache_test(function(cache) {
     var request = new Request('../resources/simple.txt');
     return assert_promise_rejects(
       cache.addAll([request, request]),
       new TypeError(),
       'Cache.addAll should throw TypeError if the same request is added ' +
       'twice.');
   }, 'Cache.addAll called with the same Request object specified twice');
 
 done();