Make window.screen property non replaceable

LayoutTests/fast/forms/page-popup/page-popup-adjust-rect.html

Index: LayoutTests/fast/forms/page-popup/page-popup-adjust-rect.html
diff --git a/LayoutTests/fast/forms/page-popup/page-popup-adjust-rect.html b/LayoutTests/fast/forms/page-popup/page-popup-adjust-rect.html
index 2be796ec5886b262deb465a17518fc61bd775ec1..29134653950eff2b144d58af449e5aa11274deb4 100644
--- a/LayoutTests/fast/forms/page-popup/page-popup-adjust-rect.html
+++ b/LayoutTests/fast/forms/page-popup/page-popup-adjust-rect.html
@@ -27,14 +27,16 @@ function makeRect(x, y, width, height) {
 }
 
 function test() {
-    popupWindow.screen = {
-        width: 80,
-        height: 60,
-        availLeft: 0,
-        availTop: 0,
-        availWidth: 80,
-        availHeight: 60,
-    };
+    Object.defineProperty(popupWindow, 'screen', {
+        value: {
+            width: 80,
+            height: 60,
+            availLeft: 0,
+            availTop: 0,
+            availWidth: 80,
+            availHeight: 60
+        }
+    });
 
     debug("Move anchor element along the vertical axis.");