[Fetch] Request.clone() should reflect body consumption.

LayoutTests/http/tests/fetch/script-tests/request.js

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
 }
 
 var URL = 'https://www.example.com/test.html';
 
 function size(headers) {
   var count = 0;
   for (var header of headers) {
     ++count;
@@ skipping 464 matching lines @@
 
     return req.text().then(function(text) {
         assert_equals(text, 'Test Blob', 'Body of request should match.');
         return req2.text();
       }).then(function(text) {
         assert_equals(text, 'Test Blob', 'Cloned request body should match.');
         return Promise.all([req.text(), req2.text()]);
       }).then(function(texts) {
         assert_equals(texts[0], '', 'The body is consumed.');
         assert_equals(texts[1], '', 'The body is consumed.');
+        return req.clone().text();
+      }).then(function(text) {
+        assert_equals(text, '', 'The body was consumed before cloned.');
       });
   }, 'Test clone behavior with loading content from Request.');
 
 async_test(function(t) {
     var request =
       new Request(URL,
                   {
                     method: 'POST',
                     body: new Blob(['Test Blob'], {type: 'test/type'})
                   });
@@ skipping 204 matching lines @@
                            body: new Blob([''], {type: 'Text/Plain'}),
                            headers: [['Content-Type', 'Text/Html']]});
     return req.blob()
       .then(function(blob) {
           assert_equals(blob.type, 'text/html');
           assert_equals(req.headers.get('Content-Type'), 'Text/Html');
         });
   }, 'Extract a MIME type (1)');
 
 done();