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

Source/core/dom/shadow/ShadowRoot.cpp

 /*
  * Copyright (C) 2011 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 144 matching lines @@
     default:
         return false;
     }
 }
 
 void ShadowRoot::recalcStyle(StyleChange change)
 {
     // ShadowRoot doesn't support custom callbacks.
     ASSERT(!hasCustomStyleCallbacks());
 
-    StyleResolver* styleResolver = document()->styleResolver();
+    StyleResolver* styleResolver = document().styleResolver();
     styleResolver->pushParentShadowRoot(this);
 
     if (!attached()) {
         attach();
         return;
     }
 
     // When we're set to lazyAttach we'll have a SubtreeStyleChange and we'll need
     // to promote the change to a Force for all our descendants so they get a
     // recalc and will attach.
@@ skipping 69 matching lines @@
 
     m_resetStyleInheritance = value;
     if (!isActive())
         return;
 
     setNeedsStyleRecalc();
 }
 
 void ShadowRoot::attach(const AttachContext& context)
 {
-    StyleResolver* styleResolver = document()->styleResolver();
+    StyleResolver* styleResolver = document().styleResolver();
     styleResolver->pushParentShadowRoot(this);
     DocumentFragment::attach(context);
     styleResolver->popParentShadowRoot(this);
 }
 
 Node::InsertionNotificationRequest ShadowRoot::insertedInto(ContainerNode* insertionPoint)
 {
     DocumentFragment::insertedInto(insertionPoint);
 
     if (!insertionPoint->inDocument() || !isOldest())
@@ skipping 138 matching lines @@
         if (element->isInsertionPoint())
             insertionPoints.append(toInsertionPoint(element));
     }
 
     ensureShadowRootRareData()->setChildInsertionPoints(insertionPoints);
 
     return m_shadowRootRareData->childInsertionPoints();
 }
 
 }