Add another body function returning a V8 Extra ReadableStream to Response

third_party/WebKit/Source/modules/fetch/Response.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // http://fetch.spec.whatwg.org/#response-class
 
 enum ResponseType { "basic", "cors", "default", "error", "opaque", "opaqueredirect" };
 
 [
     ActiveScriptWrappable,
@@ skipping 11 matching lines @@
     readonly attribute ResponseType type;
     readonly attribute USVString url;
     readonly attribute unsigned short status;
     readonly attribute boolean ok;
     readonly attribute ByteString statusText;
     readonly attribute Headers headers;
 
     [RaisesException] Response clone();
 
     [ImplementedAs=bodyWithUseCounter] readonly attribute ReadableByteStream body;
+    [RuntimeEnabled=ResponseBodyWithV8ExtraStream, CallWith=ScriptState] any v8ExtraStreamBody();
 };
 
 Response implements Body;