1 files changed, 18 insertions, 2 deletions
diff --git a/Source/WebCore/rendering/RenderScrollbarPart.h b/Source/WebCore/rendering/RenderScrollbarPart.h
index f481f5a2c..8c7a871fc 100644
--- a/Source/WebCore/rendering/RenderScrollbarPart.h
+++ b/Source/WebCore/rendering/RenderScrollbarPart.h
@@ -35,8 +35,6 @@ class RenderScrollbar;
 
 class RenderScrollbarPart : public RenderBlock {
 public:
-    friend class RenderScrollbar;
-
     RenderScrollbarPart(Node*, RenderScrollbar* = 0, ScrollbarPart = NoPart);
     virtual ~RenderScrollbarPart();
 
@@ -55,6 +53,9 @@ public:
     virtual LayoutUnit marginLeft() const { ASSERT(isIntegerValue(m_marginLeft)); return m_marginLeft; }
     virtual LayoutUnit marginRight() const { ASSERT(isIntegerValue(m_marginRight)); return m_marginRight; }
 
+    virtual bool isRenderScrollbarPart() const { return true; }
+    RenderObject* rendererOwningScrollbar() const;
+
 protected:
     virtual void styleWillChange(StyleDifference diff, const RenderStyle* newStyle);
     virtual void styleDidChange(StyleDifference, const RenderStyle* oldStyle);
@@ -71,6 +72,21 @@ private:
     ScrollbarPart m_part;
 };
 
+inline RenderScrollbarPart* toRenderScrollbarPart(RenderObject* object)
+{
+    ASSERT(!object || object->isRenderScrollbarPart());
+    return static_cast<RenderScrollbarPart*>(object);
+}
+
+inline const RenderScrollbarPart* toRenderScrollbarPart(const RenderObject* object)
+{
+    ASSERT(!object || object->isRenderScrollbarPart());
+    return static_cast<const RenderScrollbarPart*>(object);
+}
+
+// This will catch anyone doing an unnecessary cast.
+void toRenderScrollbarPart(const RenderScrollbarPart*);
+
 } // namespace WebCore
 
 #endif // RenderScrollbarPart_h