Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityMenuListOption.cpp

 /*
  * Copyright (C) 2010 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 75 matching lines @@
 bool AccessibilityMenuListOption::canSetSelectedAttribute() const
 {
     return isEnabled();
 }
 
 bool AccessibilityMenuListOption::computeAccessibilityIsIgnored() const
 {
     return accessibilityIsIgnoredByDefault();
 }
 
-LayoutRect AccessibilityMenuListOption::elementRect() const
+LayoutRect AccessibilityMenuListOption::elementRect()
 {
     AccessibilityObject* parent = parentObject();
     ASSERT(parent->isMenuListPopup());
 
     AccessibilityObject* grandparent = parent->parentObject();
     ASSERT(grandparent->isMenuList());
 
     return grandparent->elementRect();
 }
 
 String AccessibilityMenuListOption::stringValue() const
 {
     return static_cast<HTMLOptionElement*>(m_element.get())->text();
 }
 
 } // namespace WebCore