Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilitySpinButton.h

 /*
  * Copyright (C) 2011 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 33 matching lines @@
 
     void step(int amount);
     
 private:
     AccessibilitySpinButton();
 
     virtual AccessibilityRole roleValue() const { return SpinButtonRole; }
     virtual bool isSpinButton() const { return true; }
     virtual bool isNativeSpinButton() const { return true; }
     virtual void addChildren();
-    virtual LayoutRect elementRect() const;
+    virtual LayoutRect elementRect();
     
     SpinButtonElement* m_spinButtonElement;
 }; 
    
 class AccessibilitySpinButtonPart : public AccessibilityMockObject {
 public:
     static PassRefPtr<AccessibilitySpinButtonPart> create();
     virtual ~AccessibilitySpinButtonPart() { }
     
     bool isIncrementor() const { return m_isIncrementor; }
     void setIsIncrementor(bool value) { m_isIncrementor = value; }
     
 private:
     AccessibilitySpinButtonPart();
     bool m_isIncrementor : 1;
     
     virtual bool press() const;
     virtual AccessibilityRole roleValue() const { return ButtonRole; }
     virtual bool isSpinButtonPart() const { return true; }
-    virtual LayoutRect elementRect() const;
+    virtual LayoutRect elementRect();
 };
     
 inline AccessibilitySpinButton* toAccessibilitySpinButton(AccessibilityObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isNativeSpinButton());
     return static_cast<AccessibilitySpinButton*>(object);
 }
     
 inline AccessibilitySpinButtonPart* toAccessibilitySpinButtonPart(AccessibilityObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isSpinButtonPart());
     return static_cast<AccessibilitySpinButtonPart*>(object);
 }
     
 } // namespace WebCore 
 
 #endif // AccessibilitySpinButton_h