Make window.screen property non replaceable

LayoutTests/fast/js/var-declarations-shadowing.html

 <p>
 This page tests var declarations that attempt to shadow interesting global properties in
 interesting ways. <a href="http://bugs.webkit.org/show_bug.cgi?id=16644">Bug 16644</a>.
 </p>
 
 <p>
 If the test passes, you'll see a series of PASS messages below.
 </p>
 
 <pre id="console"></pre>
@@ skipping 232 matching lines @@
 
 try {
     eval("var defaultstatus = marker");
 } catch(e) { }
 shouldBe(defaultstatus == marker, "defaultstatus == marker", true);
 shouldBe(eval('defaultstatus == marker'), "eval('defaultstatus == marker')", true);
 
 try {
     eval("var screen = marker");
 } catch(e) { }
-shouldBe(screen == marker, "screen == marker", true);
-shouldBe(eval('screen == marker'), "eval('screen == marker')", true);
+shouldBe(screen == marker, "screen == marker", false);
+shouldBe(eval('screen == marker'), "eval('screen == marker')", false);
 
 try {
     eval("var history = marker");
 } catch(e) { }
 shouldBe(history == marker, "history == marker", false);
 shouldBe(eval('history == marker'), "eval('history == marker')", false);
 
 log("-----");
 
 try {
@@ skipping 38 matching lines @@
 shouldBe(crypto == marker, "crypto == marker", false);
 shouldBe(eval('crypto == marker'), "eval('crypto == marker')", false);
 
 try {
     eval("var top = marker");
 } catch(e) { }
 shouldBe(top == marker, "top == marker", false);
 shouldBe(eval('top == marker'), "eval('top == marker')", false);
 
 </script>