Remove useless null checks from Node::document() call sites

Source/core/rendering/RenderMenuList.cpp

 /*
  * This file is part of the select element renderer in WebCore.
  *
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *               2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * 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
@@ skipping 330 matching lines @@
 {
     if (m_popup)
         m_popup->hide();
 }
 
 void RenderMenuList::valueChanged(unsigned listIndex, bool fireOnChange)
 {
     // Check to ensure a page navigation has not occurred while
     // the popup was up.
     Document* doc = toElement(node())->document();
-    if (!doc || doc != doc->frame()->document())
+    if (doc != doc->frame()->document())
         return;
 
     HTMLSelectElement* select = selectElement();
     select->optionSelectedByUser(select->listToOptionIndex(listIndex), fireOnChange);
 }
 
 void RenderMenuList::listBoxSelectItem(int listIndex, bool allowMultiplySelections, bool shift, bool fireOnChangeNow)
 {
     selectElement()->listBoxSelectItem(listIndex, allowMultiplySelections, shift, fireOnChangeNow);
 }
@@ skipping 251 matching lines @@
 {
     setTextFromOption(selectElement()->listToOptionIndex(listIndex));
 }
 
 FontSelector* RenderMenuList::fontSelector() const
 {
     return document()->styleResolver()->fontSelector();
 }
 
 }