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

Source/web/ChromeClientImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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.
@@ skipping 741 matching lines @@
     setCursor(cursor);
 }
 
 void ChromeClientImpl::formStateDidChange(const Node* node)
 {
     if (m_webView->client())
         m_webView->client()->didChangeFormState(WebNode(const_cast<Node*>(node)));
 
     // The current history item is not updated yet.  That happens lazily when
     // WebFrame::currentHistoryItem is requested.
-    WebFrameImpl* webframe = WebFrameImpl::fromFrame(node->document()->frame());
+    WebFrameImpl* webframe = WebFrameImpl::fromFrame(node->document().frame());
     if (webframe->client())
         webframe->client()->didUpdateCurrentHistoryItem(webframe);
 }
 
 void ChromeClientImpl::getPopupMenuInfo(PopupContainer* popupContainer,
                                         WebPopupMenuInfo* info)
 {
     const Vector<PopupItem*>& inputItems = popupContainer->popupData();
 
     WebVector<WebMenuItemInfo> outputItems(inputItems.size());
@@ skipping 243 matching lines @@
 {
 }
 
 void NavigatorContentUtilsClientImpl::registerProtocolHandler(const String& scheme, const String& baseURL, const String& url, const String& title)
 {
     m_webView->client()->registerProtocolHandler(scheme, baseURL, url, title);
 }
 #endif
 
 } // namespace WebKit