Have Node::document() return a reference instead of a pointer

Source/core/accessibility/AccessibilitySlider.cpp

 /*
  * Copyright (C) 2009 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 65 matching lines @@
         return AccessibilityOrientationHorizontal;
     }
 }
 
 void AccessibilitySlider::addChildren()
 {
     ASSERT(!m_haveChildren);
 
     m_haveChildren = true;
 
-    AXObjectCache* cache = m_renderer->document()->axObjectCache();
+    AXObjectCache* cache = m_renderer->document().axObjectCache();
 
     AccessibilitySliderThumb* thumb = static_cast<AccessibilitySliderThumb*>(cache->getOrCreate(SliderThumbRole));
     thumb->setParent(this);
 
     // Before actually adding the value indicator to the hierarchy,
     // allow the platform to make a final decision about it.
     if (thumb->accessibilityIsIgnored())
         cache->remove(thumb->axObjectID());
     else
         m_children.append(thumb);
@@ skipping 53 matching lines @@
         return LayoutRect();
     return toElement(sliderRenderer->node())->userAgentShadowRoot()->getElementById(ShadowElementNames::sliderThumb())->boundingBox();
 }
 
 bool AccessibilitySliderThumb::computeAccessibilityIsIgnored() const
 {
     return accessibilityIsIgnoredByDefault();
 }
 
 } // namespace WebCore