[Fetch] Response.clone should tee the body stream.

LayoutTests/http/tests/fetch/script-tests/stream-reader.js

 if (self.importScripts) {
   importScripts('/fetch/resources/fetch-test-helpers.js');
 }
 
 function read_until_end(reader) {
   var chunks = [];
   function consume() {
     return reader.read().then(function(r) {
         if (r.done) {
           return chunks;
@@ skipping 87 matching lines @@
         reader = res.body.getReader();
         return reader.read();
       }).then(function(r) {
         assert_false(r.done);
         read += r.value.byteLength;
         // Make sure that we received something but we didn't receive all.
         assert_not_equals(read, 0);
         assert_not_equals(read, 190);
 
         reader.releaseLock();
-        return read_until_end(original.clone().body.getReader());
-      }).then(function(chunks) {
-        for (var chunk of chunks) {
-          read += chunk.byteLength;
+        var original_body = original.body;
+        var clone = original.clone();
+        assert_not_equals(original.body, clone.body);
+        assert_not_equals(original.body, original_body);
+        assert_not_equals(clone.body, original_body);
+        assert_throws({name: 'TypeError'}, function() {
+            original_body.getReader();
+        });
+        var reader1 = original.body.getReader();
+        var reader2 = clone.body.getReader();
+        return Promise.all([read_until_end(reader1), read_until_end(reader2)]);
+      }).then(function(r) {
+        var read1 = 0;
+        var read2 = 0;
+        for (var chunk of r[0]) {
+          read1 += chunk.byteLength;
+        }
+        for (var chunk of r[1]) {
+          read2 += chunk.byteLength;
         }
         // Make sure that we received all data in total.
-        assert_equals(read, 190);
+        assert_equals(read + read1, 190);
+        assert_equals(read + read2, 190);
       });
   }, 'Clone after reading partially');
 
 sequential_promise_test(function(t) {
     return fetch('/fetch/resources/progressive.php').then(function(res) {
         res.body.cancel();
         return res.text();
       }).then(function(text) {
         assert_equals(text, '');
       });
@@ skipping 21 matching lines @@
         assert_equals(text.length, 190);
         return stream.getReader().read();
       }).then(function(r) {
         assert_true(r.done);
         assert_equals(r.value, undefined);
       });
   }, 'Accessing body when processing text().');
 
 sequential_promise_test_done();
 done();