Allow frames with overflow:hidden scroll in slow scrolling path when scaled up

Source/core/page/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
@@ skipping 69 matching lines @@
 
     int mapFromLayoutToCSSUnits(LayoutUnit);
     LayoutUnit mapFromCSSToLayoutUnits(int);
 
     LayoutUnit marginWidth() const { return m_margins.width(); } // -1 means default
     LayoutUnit marginHeight() const { return m_margins.height(); } // -1 means default
     void setMarginWidth(LayoutUnit);
     void setMarginHeight(LayoutUnit);
 
     virtual void setCanHaveScrollbars(bool);
-    void updateCanHaveScrollbars();
 
     virtual PassRefPtr<Scrollbar> createScrollbar(ScrollbarOrientation);
 
     virtual bool avoidScrollbarCreation() const;
 
     virtual void setContentsSize(const IntSize&);
 
     void layout(bool allowSubtree = true);
     bool didFirstLayout() const;
     void layoutTimerFired(Timer<FrameView>*);
@@ skipping 160 matching lines @@
     // Methods to convert points and rects between the coordinate space of the renderer, and this view.
     virtual IntRect convertFromRenderer(const RenderObject*, const IntRect&) const;
     virtual IntRect convertToRenderer(const RenderObject*, const IntRect&) const;
     virtual IntPoint convertFromRenderer(const RenderObject*, const IntPoint&) const;
     virtual IntPoint convertToRenderer(const RenderObject*, const IntPoint&) const;
 
     bool isFrameViewScrollCorner(RenderScrollbarPart* scrollCorner) const { return m_scrollCorner == scrollCorner; }
 
     bool isScrollable();
 
-    enum ScrollbarModesCalculationStrategy { RulesFromWebContentOnly, AnyRule };
+    enum ScrollbarModesCalculationStrategy {
+        RulesFromWebContent = 1 << 0,
+        RulesFromClient = 1 << 1,
+        RulesFromVisibleContentScaleFactor = 1 << 2,
+        AnyRule = -1,
+    };
     void calculateScrollbarModesForLayout(ScrollbarMode& hMode, ScrollbarMode& vMode, ScrollbarModesCalculationStrategy = AnyRule);
 
     // Normal delay
     static void setRepaintThrottlingDeferredRepaintDelay(double p);
     // Negative value would mean that first few repaints happen without a delay
     static void setRepaintThrottlingnInitialDeferredRepaintDelayDuringLoading(double p);
     // The delay grows on each repaint to this maximum value
     static void setRepaintThrottlingMaxDeferredRepaintDelayDuringLoading(double p);
     // On each repaint the delay increses by this amount
     static void setRepaintThrottlingDeferredRepaintDelayIncrementDuringLoading(double p);
@@ skipping 305 matching lines @@
     ASSERT(!widget || widget->isFrameView());
     return static_cast<const FrameView*>(widget);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toFrameView(const FrameView*);
 
 } // namespace WebCore
 
 #endif // FrameView_h