Implement canvas focus ring methods.

Source/core/accessibility/AccessibilityRenderObject.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 196 matching lines @@
     return adoptRef(new AccessibilityRenderObject(renderer));
 }
 
 AccessibilityRenderObject::~AccessibilityRenderObject()
 {
     ASSERT(isDetached());
 }
 
 LayoutRect AccessibilityRenderObject::elementRect() const
 {
+    if (!m_explicitElementRect.isEmpty())
+        return m_explicitElementRect;
     if (!m_renderer)
         return LayoutRect();
     if (!m_renderer->isBox())
         return computeElementRect();
 
     for (const AccessibilityObject* obj = this; obj; obj = obj->parentObject()) {
         if (obj->isAccessibilityRenderObject())
             static_cast<const AccessibilityRenderObject*>(obj)->checkCachedElementRect();
     }
     for (const AccessibilityObject* obj = this; obj; obj = obj->parentObject()) {
@@ skipping 2284 matching lines @@
         if (label && label->renderer()) {
             LayoutRect labelRect = axObjectCache()->getOrCreate(label)->elementRect();
             result.unite(labelRect);
         }
     }
 
     return result;
 }
 
 } // namespace WebCore