Make window.screen property non replaceable

Source/core/frame/Screen.h

Index: Source/core/frame/Screen.h
diff --git a/Source/core/frame/Screen.h b/Source/core/frame/Screen.h
index d03653e14bfafa21a69033a3e36b64cde265522e..ad2ed2bab4237415c1bf7f58a644eadc3a8432cc 100644
--- a/Source/core/frame/Screen.h
+++ b/Source/core/frame/Screen.h
@@ -40,6 +40,7 @@
 
 namespace WebCore {
 
+    class Dictionary;
     class LocalFrame;
 
     class Screen FINAL : public RefCountedWillBeRefCountedGarbageCollected<Screen>, public ScriptWrappable, public EventTargetWithInlineData, public DOMWindowProperty, public WillBeHeapSupplementable<Screen> {
@@ -66,6 +67,10 @@ namespace WebCore {
 
         void trace(Visitor*);
 
+        // For layout tests.
+        static void setOverrideScreenData(const Dictionary&);
+        static void clearOverrideScreenData();
+
     private:
         explicit Screen(LocalFrame*);
     };