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

Source/core/rendering/RenderTheme.cpp

 /**
  * This file is part of the theme implementation for form controls in WebCore.
  *
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 785 matching lines @@
         result |= IndeterminateState;
     return result;
 }
 
 bool RenderTheme::isActive(const RenderObject* o) const
 {
     Node* node = o->node();
     if (!node)
         return false;
 
-    Page* page = node->document()->page();
+    Page* page = node->document().page();
     if (!page)
         return false;
 
     return page->focusController().isActive();
 }
 
 bool RenderTheme::isChecked(const RenderObject* o) const
 {
     if (!o->node() || !o->node()->hasTagName(inputTag))
         return false;
@@ skipping 15 matching lines @@
     return !toElement(node)->isDisabledFormControl();
 }
 
 bool RenderTheme::isFocused(const RenderObject* o) const
 {
     Node* node = o->node();
     if (!node)
         return false;
 
     node = node->focusDelegate();
-    Document* document = node->document();
-    Frame* frame = document->frame();
-    return node == document->focusedElement() && node->shouldHaveFocusAppearance() && frame && frame->selection()->isFocusedAndActive();
+    Document& document = node->document();
+    Frame* frame = document.frame();
+    return node == document.focusedElement() && node->shouldHaveFocusAppearance() && frame && frame->selection()->isFocusedAndActive();
 }
 
 bool RenderTheme::isPressed(const RenderObject* o) const
 {
     if (!o->node())
         return false;
     return o->node()->active();
 }
 
 bool RenderTheme::isSpinUpButtonPartPressed(const RenderObject* o) const
@@ skipping 544 matching lines @@
 
     // padding - not honored by WinIE, needs to be removed.
     style->resetPadding();
 
     // border - honored by WinIE, but looks terrible (just paints in the control box and turns off the Windows XP theme)
     // for now, we will not honor it.
     style->resetBorder();
 }
 
 } // namespace WebCore