Cleanup <static_cast>: Switch to toFoo for Accessibility Objects.

Source/core/platform/Scrollbar.h

 /*
  * Copyright (C) 2004, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 174 matching lines @@
 
     bool m_isAlphaLocked;
 
 private:
     virtual bool isScrollbar() const { return true; }
     virtual AXObjectCache* existingAXObjectCache() const;
 
     float scrollableAreaCurrentPos() const;
 };
 
+inline Scrollbar* toScrollbar(Widget* widget)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!widget || widget->isScrollbar());
+    return static_cast<Scrollbar*>(widget);
+}
+
+inline const Scrollbar* toScrollbar(const Widget* widget)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!widget || widget->isScrollbar());
+    return static_cast<const Scrollbar*>(widget);
+}
+
+// This will catch anyone doing an unnecessary cast.
+void toScrollbar(const Scrollbar*);
+
 } // namespace WebCore
 
 #endif // Scrollbar_h