Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityScrollbar.cpp

 /*
  * Copyright (C) 2010 Apple 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
@@ skipping 26 matching lines @@
     : m_scrollbar(scrollbar)
 {
     ASSERT(scrollbar);
 }
 
 PassRefPtr<AccessibilityScrollbar> AccessibilityScrollbar::create(Scrollbar* scrollbar)
 {
     return adoptRef(new AccessibilityScrollbar(scrollbar));
 }
     
-LayoutRect AccessibilityScrollbar::elementRect() const
+LayoutRect AccessibilityScrollbar::elementRect()
 {
     if (!m_scrollbar)
         return LayoutRect();
     
     return m_scrollbar->frameRect();
 }
     
 Document* AccessibilityScrollbar::document() const
 {
     AccessibilityObject* parent = parentObject();
     if (!parent)
         return 0;
     return parent->document();
 }
 
-AccessibilityOrientation AccessibilityScrollbar::orientation() const
+AccessibilityOrientation AccessibilityScrollbar::orientation()
 {
     if (!m_scrollbar)
         return AccessibilityOrientationHorizontal;
 
     if (m_scrollbar->orientation() == HorizontalScrollbar)
         return AccessibilityOrientationHorizontal;
     if (m_scrollbar->orientation() == VerticalScrollbar)
         return AccessibilityOrientationVertical;
 
     return AccessibilityOrientationHorizontal;
@@ skipping 20 matching lines @@
         return;
     
     if (!m_scrollbar->scrollableArea())
         return;
 
     float newValue = value * m_scrollbar->maximum();
     m_scrollbar->scrollableArea()->scrollToOffsetWithoutAnimation(m_scrollbar->orientation(), newValue);
 }
     
 } // namespace WebCore