Simplify and add caching for accessible bounding box calculation.

Source/core/accessibility/AccessibilityRenderObject.h

Index: Source/core/accessibility/AccessibilityRenderObject.h
diff --git a/Source/core/accessibility/AccessibilityRenderObject.h b/Source/core/accessibility/AccessibilityRenderObject.h
index 839c24c4f99a1a83b5c01e4ba37007e052def8da..1c423ebc9d9229b857355b0884f4f94e8611609a 100644
--- a/Source/core/accessibility/AccessibilityRenderObject.h
+++ b/Source/core/accessibility/AccessibilityRenderObject.h
@@ -63,8 +63,6 @@ public:
     static PassRefPtr<AccessibilityRenderObject> create(RenderObject*);
     virtual ~AccessibilityRenderObject();
 
-    RenderObject* m_renderer;
-
     // Public, overridden from AccessibilityObject.
     virtual RenderObject* renderer() const { return m_renderer; }
     virtual LayoutRect elementRect() const;
@@ -83,6 +81,12 @@ public:
     virtual AccessibilityRole determineAccessibilityRole();
 
 protected:
+    RenderObject* m_renderer;
+    mutable LayoutRect m_cachedElementRect;
+    mutable LayoutRect m_cachedFrameRect;
+    mutable IntPoint m_cachedScrollPosition;
+    mutable bool m_cachedElementRectDirty;
+
     //
     // Overridden from AccessibilityObject.
     //
@@ -140,7 +144,6 @@ protected:
 
     // Properties of interactive elements.
     virtual const String& actionVerb() const;
-    LayoutRect checkboxOrRadioRect() const;
     virtual void selectedChildren(AccessibilityChildrenVector&);
     virtual String stringValue() const;
 
@@ -171,8 +174,10 @@ protected:
     // Accessibility Text - (To be deprecated).
     virtual String helpText() const;
 
-    // Position and size.
-    virtual LayoutRect boundingBoxRect() const;
+    // Location and click point in frame-relative coordinates.
+    virtual void checkCachedElementRect() const;
+    virtual void updateCachedElementRect() const;
+    virtual void markCachedElementRectDirty() const;
     virtual IntPoint clickPoint();
 
     // Hit testing.
@@ -272,6 +277,7 @@ private:
     void ariaSelectedRows(AccessibilityChildrenVector&);
     bool elementAttributeValue(const QualifiedName&) const;
     bool inheritsPresentationalRole() const;
+    LayoutRect computeElementRect() const;
 };
 
 inline AccessibilityRenderObject* toAccessibilityRenderObject(AccessibilityObject* object)