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

Source/core/editing/EditorCommand.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Igalia S.L.
  *
  * 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.
@@ skipping 78 matching lines @@
 // Related to Editor::selectionForCommand.
 // Certain operations continue to use the target control's selection even if the event handler
 // already moved the selection outside of the text control.
 static Frame* targetFrame(Frame& frame, Event* event)
 {
     if (!event)
         return &frame;
     Node* node = event->target()->toNode();
     if (!node)
         return &frame;
-    return node->document()->frame();
+    return node->document().frame();
 }
 
 static bool applyCommandToFrame(Frame& frame, EditorCommandSource source, EditAction action, StylePropertySet* style)
 {
     // FIXME: We don't call shouldApplyStyle when the source is DOM; is there a good reason for that?
     switch (source) {
     case CommandFromMenuOrKeyBinding:
         frame.editor().applyStyleToSelection(style, action);
         return true;
     case CommandFromDOM:
@@ skipping 1632 matching lines @@
         return m_command->state(*m_frame, triggeringEvent) == TrueTriState ? "true" : "false";
     return m_command->value(*m_frame, triggeringEvent);
 }
 
 bool Editor::Command::isTextInsertion() const
 {
     return m_command && m_command->isTextInsertion;
 }
 
 } // namespace WebCore