Make window.navigator property non replaceable

Source/core/frame/Window.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 24 matching lines @@
 ] interface Window : EventTarget {
     // DOM Level 0
     [Replaceable] readonly attribute Screen screen;
     [Replaceable] readonly attribute History history;
     [Replaceable] readonly attribute BarProp locationbar;
     [Replaceable] readonly attribute BarProp menubar;
     [Replaceable] readonly attribute BarProp personalbar;
     [Replaceable] readonly attribute BarProp scrollbars;
     [Replaceable] readonly attribute BarProp statusbar;
     [Replaceable] readonly attribute BarProp toolbar;
-    [Replaceable, PerWorldBindings, ActivityLogging=GetterForIsolatedWorlds] readonly attribute Navigator navigator;
+    [PerWorldBindings, ActivityLogging=GetterForIsolatedWorlds] readonly attribute Navigator navigator;
     [Replaceable] readonly attribute Navigator clientInformation;
     [DoNotCheckSecurity, Unforgeable, Replaceable, PerWorldBindings, ActivityLogging=ForIsolatedWorlds, PutForwards=href] readonly attribute Location location;
     [Custom, MeasureAs=WindowEvent, NotEnumerable] attribute Event event;
 
     Selection getSelection();
 
     [CheckSecurity=Node, Custom=Getter] readonly attribute Element frameElement;
 
     [DoNotCheckSecurity, CallWith=ExecutionContext] void focus();
     [DoNotCheckSecurity] void blur();
@@ skipping 174 matching lines @@
 
     [NotEnumerable] getter Window (unsigned long index);
     [Custom, NotEnumerable] getter Window (DOMString name);
 };
 
 Window implements GlobalEventHandlers;
 Window implements ImageBitmapFactories;
 Window implements WindowBase64;
 Window implements WindowEventHandlers;
 Window implements WindowTimers;