Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityTableColumn.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 41 matching lines @@
     return adoptRef(new AccessibilityTableColumn());
 }
 
 void AccessibilityTableColumn::setParent(AccessibilityObject* parent)
 {
     AccessibilityMockObject::setParent(parent);
     
     clearChildren();
 }
     
-LayoutRect AccessibilityTableColumn::elementRect() const
+LayoutRect AccessibilityTableColumn::elementRect()
 {
     // this will be filled in when addChildren is called
     return m_columnRect;
 }
 
 AccessibilityObject* AccessibilityTableColumn::headerObject()
 {
     if (!m_parent)
         return 0;
     
@@ skipping 103 matching lines @@
         // make sure the last one isn't the same as this one (rowspan cells)
         if (m_children.size() > 0 && m_children.last() == cell)
             continue;
             
         m_children.append(cell);
         m_columnRect.unite(cell->elementRect());
     }
 }
     
 } // namespace WebCore