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

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

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
 }
 
 function size(headers) {
   var count = 0;
   for (var header of headers) {
     ++count;
   }
   return count;
 }
 
 function consume(reader) {
   var chunks = [];
   function rec(reader) {
     return reader.read().then(function(r) {
         if (r.done) {
           return chunks;
         }
         chunks.push(r.value);
         return rec(reader);
       });
   }
   return rec(reader);
 }
 
-function flatten(chunks) {
-  var size = 0;
+function decode(chunks) {
+  var decoder = new TextDecoder();
+  var result = '';
   for (var chunk of chunks) {
-    size += chunk.byteLength;
+    result += decoder.decode(chunk, {stream: true});
   }
-  var buffer = new Uint8Array(size);
-  var current = 0;
-  for (var chunk of chunks) {
-    buffer.set(chunk, 0);
-  }
-  return buffer;
+  result += decoder.decode(new Uint8Array(0));
+  return result;
 }
 
 test(function() {
     var response = new Response(new Blob());
     assert_equals(response.type, 'default',
                   'Default Response.type should be \'default\'');
     assert_equals(response.url, '', 'Response.url should be the empty string');
     assert_equals(response.status, 200,
                   'Default Response.status should be 200');
     assert_true(response.ok, 'Default Response.ok must be true');
@@ skipping 241 matching lines @@
             new Response(new Blob(), {statusText: text});
           },
           'new Response with invalid statusText (' + text +
           ') must throw');
       });
   }, 'Response throw error test');
 
 promise_test(function(t) {
     var res = new Response('hello');
     return consume(res.body.getReader()).then(function(chunks) {
-        return flatten(chunks);
-      }).then(function(view) {
-        assert_equals(new TextDecoder().decode(view), 'hello');
+        return decode(chunks);
+      }).then(function(text) {
+        assert_equals(text, 'hello');
         return res.body.getReader().read();
       }).then(function(r) {
         assert_true(r.done);
         return res.text();
       }).then(function(r) {
         assert_equals(r, '');
       });
   }, 'Read Response body via stream');
 
 promise_test(function(t) {
@@ skipping 30 matching lines @@
       }).then(function(buffer) {
         assert_equals(buffer.byteLength + head.byteLength, size);
         return res.body.getReader().read();
       }).then(function(r) {
         assert_true(r.done);
       });
   }, 'Partial read on Response');
 
 promise_test(function(t) {
     var res = new Response('hello');
+    var body = res.body;
     var clone = res.clone();
+    assert_not_equals(res.body, body);
+    assert_not_equals(res.body, clone.body);
+    assert_not_equals(body, clone.body);
+    assert_throws({name: 'TypeError'}, function() { body.getReader(); });
     return Promise.all([res.text(), clone.text()]).then(function(r) {
         assert_equals(r[0], 'hello');
         assert_equals(r[1], 'hello');
       });
-  }, 'Clone on Response');
+  }, 'Clone on Response (text)');
 
 promise_test(function(t) {
     var res = new Response('hello');
+    var body = res.body;
+    var clone = res.clone();
+    assert_not_equals(res.body, body);
+    assert_not_equals(res.body, clone.body);
+    assert_not_equals(body, clone.body);
+    assert_throws({name: 'TypeError'}, function() { body.getReader(); });
+    var reader1 = res.body.getReader();
+    var reader2 = clone.body.getReader();
+    return Promise.all([consume(reader1), consume(reader2)]).then(function(r) {
+        assert_equals(decode(r[0]), 'hello');
+        assert_equals(decode(r[1]), 'hello');
+      });
+  }, 'Clone on Response (manual read)');
+
+promise_test(function(t) {
+    var res = new Response('hello');
     var clone = res.clone();
     res.body.cancel();
     return Promise.all([res.text(), clone.text()]).then(function(r) {
         assert_equals(r[0], '');
         assert_equals(r[1], 'hello');
       });
   }, 'Clone and Cancel on Response');
 
 promise_test(function(t) {
     var res = new Response('hello');
@@ skipping 98 matching lines @@
     res.body.cancel();
     res = res.clone();
     return res.blob()
       .then(function(blob) {
           assert_equals(blob.type, 'text/html');
           assert_equals(res.headers.get('Content-Type'), 'Text/Html');
         });
   }, 'Extract a MIME type (3)');
 
 done();