[Fetch] Request constructor 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 687 matching lines @@
                           {method: 'POST',
                            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)');
 
+promise_test(function(t) {
+    var req = new Request('http://localhost/', {method: 'POST', body: 'hello'});
+    return req.text().then(function(text) {
+        assert_equals(text, 'hello');
+        var req2 = new Request(req);
+        assert_true(req.bodyUsed);
+        assert_false(req2.bodyUsed);
+        return req2.text();
+      }).then(function(text) {
+        assert_equals(text, '');
+      });
+  }, 'Consume and pass');
+
 done();