Avoid calling slower Node::firstChild() / Node::lastChild() when possible

Source/core/dom/Range.cpp

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * (C) 2000 Gunnstein Lye (gunnstein@netcom.no)
  * (C) 2000 Frederik Holljen (frederik.holljen@hig.no)
  * (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Motorola Mobility. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 854 matching lines @@
     if (startIsText)
         checkAgainst = m_start.container()->parentNode();
     else
         checkAgainst = m_start.container();
 
     Node::NodeType newNodeType = newNode->nodeType();
     int numNewChildren;
     if (newNodeType == Node::DOCUMENT_FRAGMENT_NODE && !newNode->isShadowRoot()) {
         // check each child node, not the DocumentFragment itself
         numNewChildren = 0;
-        for (Node* c = newNode->firstChild(); c; c = c->nextSibling()) {
+        for (Node* c = toDocumentFragment(newNode)->firstChild(); c; c = c->nextSibling()) {
             if (!checkAgainst->childTypeAllowed(c->nodeType())) {
                 exceptionState.throwDOMException(HierarchyRequestError, "The node to be inserted contains a '" + c->nodeName() + "' node, which may not be inserted here.");
                 return;
             }
             ++numNewChildren;
         }
     } else {
         numNewChildren = 1;
         if (!checkAgainst->childTypeAllowed(newNodeType)) {
             exceptionState.throwDOMException(HierarchyRequestError, "The node to be inserted is a '" + newNode->nodeName() + "' node, which may not be inserted here.");
@@ skipping 32 matching lines @@
             return;
 
         container = m_start.container();
         container->parentNode()->insertBefore(newNode.release(), newText.get(), exceptionState);
         if (exceptionState.hadException())
             return;
 
         if (collapsed)
             m_end.setToBeforeChild(*newText);
     } else {
-        RefPtrWillBeRawPtr<Node> lastChild = (newNodeType == Node::DOCUMENT_FRAGMENT_NODE) ? newNode->lastChild() : newNode.get();
+        RefPtrWillBeRawPtr<Node> lastChild = (newNodeType == Node::DOCUMENT_FRAGMENT_NODE) ? toDocumentFragment(newNode)->lastChild() : newNode.get();
         if (lastChild && lastChild == m_start.childBefore()) {
             // The insertion will do nothing, but we need to extend the range to include
             // the inserted nodes.
-            Node* firstChild = (newNodeType == Node::DOCUMENT_FRAGMENT_NODE) ? newNode->firstChild() : newNode.get();
+            Node* firstChild = (newNodeType == Node::DOCUMENT_FRAGMENT_NODE) ? toDocumentFragment(newNode)->firstChild() : newNode.get();
             ASSERT(firstChild);
             m_start.setToBeforeChild(*firstChild);
             return;
         }
 
         container = m_start.container();
         container->insertBefore(newNode.release(), container->traverseToChildAt(m_start.offset()), exceptionState);
         if (exceptionState.hadException())
             return;
 
@@ skipping 751 matching lines @@
 
 void showTree(const WebCore::Range* range)
 {
     if (range && range->boundaryPointsValid()) {
         range->startContainer()->showTreeAndMark(range->startContainer(), "S", range->endContainer(), "E");
         fprintf(stderr, "start offset: %d, end offset: %d\n", range->startOffset(), range->endOffset());
     }
 }
 
 #endif