[Fetch] Check / Set .bodyUsed in Request construction if the src body is null.

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';
 
 test(function() {
     var headers = new Headers;
     headers.set('User-Agent', 'Mozilla/5.0');
     headers.set('Accept', 'text/html');
@@ skipping 254 matching lines @@
                       'method should not be changed when normalized: ' +
                       method);
       });
   }, 'Request: valid method names and normalize test');
 
 test(function() {
     var req = new Request(URL);
     assert_false(req.bodyUsed,
                  'Request should not be flagged as used if it has not been ' +
                  'consumed.');
+    // See https://crbug.com/501195.
     var req2 = new Request(req);
-    assert_false(req.bodyUsed,
-                'Request should not be flagged as used if it does not have' +
+    assert_true(req.bodyUsed,
+                'Request should be flagged as used if it does not have' +
                 'body.');
     assert_false(req2.bodyUsed,
                  'Request should not be flagged as used if it has not been ' +
                  'consumed.');
   }, 'Request construction without body behavior regardning "bodyUsed"');
 
 test(function() {
     var req = new Request(URL, {method: 'POST', body: 'hello'});
     assert_false(req.bodyUsed,
                  'Request should not be flagged as used if it has not been ' +
                  'consumed.');
     var req2 = new Request(req);
     assert_true(req.bodyUsed,
                 'Request should be flagged as used if it has been consumed.');
     assert_false(req2.bodyUsed,
                  'Request should not be flagged as used if it has not been ' +
                  'consumed.');
-    // Now we can create a Request from |req|, because creating |req2| from
-    // |req| sets |req|'s body to null as specified.
-    var req3 = new Request(req);
-    assert_true(req.bodyUsed,
-                'Request should be flagged as used if it has been consumed.');
+    // See https://crbug.com/501195.
+    assert_throws(
+      {name: 'TypeError'},
+      function() { new Request(req); },
+      'Request construction should throw if used.');
   }, 'Request construction without body behavior regardning "bodyUsed"');
 
 test(function() {
     var req = new Request(URL, {method: 'POST', body: 'hello'});
     assert_false(req.bodyUsed,
                  'Request should not be flagged as used if it has not been ' +
                  'consumed.');
     assert_throws(
       {name: 'TypeError'},
       function() { new Request(req, {method: 'GET'}); },
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 // Tests for requests context.
 test(function() {
     var request = new Request('http://localhost/', {method: 'POST', body: ''});
     assert_equals(request.context, '',
                   'Request.context should be empty string ' +
                   'for synthetic Request object');
   }, 'RequestContext of a synthetic Request object');
 
 done();