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

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 455 matching lines @@
         headers: headers,
         body: new Blob(['Test Blob'], {type: 'test/type'})
       });
     var req2 = req.clone();
     // Change headers and of original request.
     req.headers.set('Content-Language', 'en');
     assert_equals(req2.headers.get('Content-Language'), 'ja',
                   'Headers of cloned request should not change when ' +
                   'original request headers are changed.');
 
-    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 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.');
+      });
   }, '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'})
                   });
     assert_equals(
@@ skipping 203 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();