Replace window.external with a v8::extension.

chrome/renderer/external_extension.h

Index: chrome/renderer/external_extension.h
===================================================================
--- chrome/renderer/external_extension.h	(revision 0)
+++ chrome/renderer/external_extension.h	(revision 0)
@@ -0,0 +1,21 @@
+// Copyright (c) 2009 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.
+
+// Implements the window.external object.
+
+#ifndef CHROME_RENDERER_EXTENSIONS_V8_EXTERNAL_EXTENSION_H_
+#define CHROME_RENDERER_EXTENSIONS_V8_EXTERNAL_EXTENSION_H_
+
+#include "v8/include/v8.h"
+
+namespace extensions_v8 {
+
+class ExternalExtension {
+ public:
+  static v8::Extension* Get();
+};
+
+}  // namespace extensions_v8
+
+#endif  // CHROME_RENDERER_EXTENSIONS_V8_EXTERNAL_EXTENSION_H_