Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityTableHeaderContainer.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 29 matching lines @@
 
 AccessibilityTableHeaderContainer::~AccessibilityTableHeaderContainer()
 {
 }
 
 PassRefPtr<AccessibilityTableHeaderContainer> AccessibilityTableHeaderContainer::create()
 {
     return adoptRef(new AccessibilityTableHeaderContainer());
 }
     
-LayoutRect AccessibilityTableHeaderContainer::elementRect() const
+LayoutRect AccessibilityTableHeaderContainer::elementRect()
 {
     // this will be filled in when addChildren is called
     return m_headerRect;
 }
 
 bool AccessibilityTableHeaderContainer::computeAccessibilityIsIgnored() const
 {
     if (!m_parent)
         return true;
 
     return m_parent->accessibilityIsIgnored();
 }
 
 void AccessibilityTableHeaderContainer::addChildren()
 {
     ASSERT(!m_haveChildren); 
     
     m_haveChildren = true;
     if (!m_parent || !m_parent->isAccessibilityTable())
         return;
     
     static_cast<AccessibilityTable*>(m_parent)->columnHeaders(m_children);
     
     unsigned length = m_children.size();
     for (unsigned k = 0; k < length; ++k)
         m_headerRect.unite(m_children[k]->elementRect());
 }
 
 } // namespace WebCore