Have ElementTraversal::firstWithin() take a reference

Source/core/css/StyleInvalidationAnalysis.cpp

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 186 matching lines @@
     if (classScopes.isEmpty() || !element->hasClass())
         return false;
     const SpaceSplitString& classNames = element->classNames();
     for (unsigned i = 0; i < classNames.size(); ++i) {
         if (classScopes.contains(classNames[i].impl()))
             return true;
     }
     return false;
 }
 
-void StyleInvalidationAnalysis::invalidateStyle(Document* document)
+void StyleInvalidationAnalysis::invalidateStyle(Document& document)
 {
     ASSERT(!m_dirtiesAllStyle);
 
     if (!m_scopingNodes.isEmpty()) {
         for (unsigned i = 0; i < m_scopingNodes.size(); ++i)
             m_scopingNodes.at(i)->setNeedsStyleRecalc();
     }
 
     if (m_idScopes.isEmpty() && m_classScopes.isEmpty())
         return;
     Element* element = ElementTraversal::firstWithin(document);
     while (element) {
         if (elementMatchesSelectorScopes(element, m_idScopes, m_classScopes)) {
             element->setNeedsStyleRecalc();
             // The whole subtree is now invalidated, we can skip to the next sibling.
             element = ElementTraversal::nextSkippingChildren(*element);
             continue;
         }
         element = ElementTraversal::next(*element);
     }
 }
 
 }