Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityNodeObject.h

 /*
  * Copyright (C) 2012, Google 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 153 matching lines @@
     // Accessibility Text.
     virtual void accessibilityText(Vector<AccessibilityText>&);
     virtual String textUnderElement() const;
 
     // Accessibility Text - (To be deprecated).
     virtual String accessibilityDescription() const;
     virtual String title() const;
     virtual String helpText() const;
 
     // Position and size.
-    virtual LayoutRect boundingBoxRect() const;
-    virtual LayoutRect elementRect() const;
+    virtual LayoutRect elementRect();
 
     // High-level accessibility tree access.
     virtual AccessibilityObject* parentObject() const;
     virtual AccessibilityObject* parentObjectIfExists() const;
 
     // Low-level accessibility tree exploration.
     virtual AccessibilityObject* firstChild() const;
     virtual AccessibilityObject* lastChild() const;
     virtual AccessibilityObject* previousSibling() const;
     virtual AccessibilityObject* nextSibling() const;
@@ skipping 40 matching lines @@
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isAccessibilityNodeObject());
     return static_cast<const AccessibilityNodeObject*>(object);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toAccessibilityNodeObject(const AccessibilityNodeObject*);
 
 } // namespace WebCore
 
 #endif // AccessibilityNodeObject_h