Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityScrollView.cpp

 /*
  * Copyright (C) 2011 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 169 matching lines @@
         return 0;
     
     if (m_horizontalScrollbar && m_horizontalScrollbar->elementRect().contains(point))
         return m_horizontalScrollbar.get();
     if (m_verticalScrollbar && m_verticalScrollbar->elementRect().contains(point))
         return m_verticalScrollbar.get();
     
     return webArea->accessibilityHitTest(point);
 }
 
-LayoutRect AccessibilityScrollView::elementRect() const
+LayoutRect AccessibilityScrollView::elementRect()
 {
     if (!m_scrollView)
         return LayoutRect();
 
     return m_scrollView->frameRect();
 }
 
 FrameView* AccessibilityScrollView::documentFrameView() const
 {
     if (!m_scrollView || !m_scrollView->isFrameView())
@@ skipping 31 matching lines @@
     return m_scrollView;
 }
 
 void AccessibilityScrollView::scrollTo(const IntPoint& point) const
 {
     if (m_scrollView)
         m_scrollView->setScrollPosition(point);
 }
 
 } // namespace WebCore