Support [Replaceable] for screen, pageXOffset, pageYOffset

Source/core/frame/Window.idl

Index: Source/core/frame/Window.idl
diff --git a/Source/core/frame/Window.idl b/Source/core/frame/Window.idl
index a77a67947ffeafcf391ccb3340748a1d5326ed79..896a44fac70d5edf0d04b37addaec1a5ad30e4f3 100644
--- a/Source/core/frame/Window.idl
+++ b/Source/core/frame/Window.idl
@@ -105,7 +105,7 @@
     // CSSOM View Module
     // http://dev.w3.org/csswg/cssom-view/#extensions-to-the-window-interface
     [NewObject] MediaQueryList matchMedia(DOMString query);
-    [SameObject] readonly attribute Screen screen;
+    [SameObject, Replaceable] readonly attribute Screen screen;
 
     // browsing context
     // FIXME: The x and y arguments should not be optional. crbug.com/453421
@@ -115,15 +115,14 @@
     void resizeBy(optional long x, optional long y);
 
     // viewport
-    // FIXME: None of the CCSOM View Module attributes should be [Replaceable].
     [Replaceable] readonly attribute long innerWidth;
     [Replaceable] readonly attribute long innerHeight;
 
     // viewport scrolling
     [Replaceable] readonly attribute double scrollX;
-    readonly attribute double pageXOffset;
+    [Replaceable] readonly attribute double pageXOffset;
     [Replaceable] readonly attribute double scrollY;
-    readonly attribute double pageYOffset;
+    [Replaceable] readonly attribute double pageYOffset;
     [RuntimeEnabled=CSSOMSmoothScroll] void scroll(optional ScrollToOptions options);
     void scroll(unrestricted double x, unrestricted double y);
     [RuntimeEnabled=CSSOMSmoothScroll] void scrollTo(optional ScrollToOptions options);