Remove frame flattening support as Chromium has no intention of using it

Source/WebCore/page/FrameView.h

Index: Source/WebCore/page/FrameView.h
diff --git a/Source/WebCore/page/FrameView.h b/Source/WebCore/page/FrameView.h
index 9d8b22e1b5bc64284bb93fed4b6ac46d716a7ce0..cae8c8f656b0d8fb606511df4d7d032841cde1d7 100644
--- a/Source/WebCore/page/FrameView.h
+++ b/Source/WebCore/page/FrameView.h
@@ -90,8 +90,6 @@ public:
 
     virtual PassRefPtr<Scrollbar> createScrollbar(ScrollbarOrientation);
 
-    virtual bool avoidScrollbarCreation() const;
-
     virtual void setContentsSize(const IntSize&);
 
     void layout(bool allowSubtree = true);
@@ -245,8 +243,6 @@ public:
 
     Color documentBackgroundColor() const;
 
-    bool isInChildFrameWithFrameFlattening() const;
-
     static double currentPaintTimeStamp() { return sCurrentPaintTimeStamp; } // returns 0 if not painting
     
     void updateLayoutAndStyleIfNeededRecursive();
@@ -440,8 +436,6 @@ private:
 
     FrameView* parentFrameView() const;
 
-    bool doLayoutWithFrameFlattening(bool allowSubtree);
-
     virtual AXObjectCache* axObjectCache() const;
     void notifyWidgetsInAllFrames(WidgetNotification);
     void removeFromAXObjectCache();