Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityImageMapLink.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 113 matching lines @@
     const AtomicString& title = getAttribute(titleAttr);
     if (!title.isEmpty())
         return title;
     const AtomicString& summary = getAttribute(summaryAttr);
     if (!summary.isEmpty())
         return summary;
 
     return String();
 }
 
-LayoutRect AccessibilityImageMapLink::elementRect() const
+LayoutRect AccessibilityImageMapLink::elementRect()
 {
     if (!m_mapElement.get() || !m_areaElement.get())
         return LayoutRect();
 
     RenderObject* renderer;
     if (m_parent && m_parent->isAccessibilityRenderObject())
         renderer = static_cast<AccessibilityRenderObject*>(m_parent)->renderer();
     else
         renderer = m_mapElement->renderer();
     
     if (!renderer)
         return LayoutRect();
     
     return m_areaElement->computeRect(renderer);
 }
     
 } // namespace WebCore