Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityListBox.cpp

 /*
  * Copyright (C) 2008 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 142 matching lines @@
 {
     // the internal HTMLSelectElement methods for returning a listbox option at a point
     // ignore optgroup elements.
     if (!m_renderer)
         return 0;
     
     Node* node = m_renderer->node();
     if (!node)
         return 0;
     
-    LayoutRect parentRect = boundingBoxRect();
+    LayoutRect parentRect = elementRect();
     
     AccessibilityObject* listBoxOption = 0;
     unsigned length = m_children.size();
     for (unsigned i = 0; i < length; i++) {
         LayoutRect rect = toRenderListBox(m_renderer)->itemBoundingBoxRect(parentRect.location(), i);
         // The cast to HTMLElement below is safe because the only other possible listItem type
         // would be a WMLElement, but WML builds don't use accessibility features at all.
         if (rect.contains(point)) {
             listBoxOption = m_children[i].get();
             break;
         }
     }
     
     if (listBoxOption && !listBoxOption->accessibilityIsIgnored())
         return listBoxOption;
     
     return axObjectCache()->getOrCreate(m_renderer);
 }
 
 } // namespace WebCore