Make window.navigator property non replaceable

LayoutTests/fast/dom/Window/get-set-properties.html

 <p>This page tests getting and setting window properties and functions.</p>
 <pre id="console"></pre>
 
 <script>
 function log(s)
 {
     document.getElementById("console").appendChild(document.createTextNode(s + "\n"));
 }
 
 function shouldBe(a, b)
@@ skipping 173 matching lines @@
     "console", 
     "devicePixelRatio", 
     "event", 
     "frames",
     "history",
     "innerHeight", 
     "innerWidth", 
     "length",
     "locationbar", 
     "menubar", 
-    "navigator", 
     "offscreenBuffering", 
     "opener",
     "outerHeight", 
     "outerWidth", 
     "parent",
     "personalbar",
     "screenLeft", 
     "screenTop", 
     "screenX", 
     "screenY", 
     "scrollX", 
     "scrollY", 
     "scrollbars",
     "self",
     "statusbar",
     "toolbar"
 ];
 
 var windowReadOnlyProperties = [
     "closed",
     "document",
+    "navigator",
     "pageXOffset",
     "pageYOffset",
     "window",
     "top"
 ];
 
 var windowReadWriteStringProperties = [
     "defaultStatus",
     "defaultstatus",
     "name",
@@ skipping 93 matching lines @@
 
     log("\n----- tests for getting/setting event handlers -----\n");
 
     for (var i = 0; i < windowEventHandlers.length; i++) {
         var property = windowEventHandlers[i];
         shouldBeTrue("canGet('" + property + "')");
         shouldBeTrue("canSetWithCallable('" + property + "')");
     }
 }
 </script>