Move implementation of Range::firstNode and Range::pastLastNode to Position

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 1396 matching lines @@
     for (Node* n = firstNode(); n != pastLast; n = NodeTraversal::next(*n)) {
         if (n->isDocumentTypeNode()) {
             exceptionState.throwDOMException(HierarchyRequestError, "The Range contains a doctype node.");
             return;
         }
     }
 }
 
 Node* Range::firstNode() const
 {
-    if (m_start.container()->offsetInCharacters())
-        return m_start.container();
-    if (Node* child = NodeTraversal::childAt(*m_start.container(), m_start.offset()))
-        return child;
-    if (!m_start.offset())
-        return m_start.container();
-    return NodeTraversal::nextSkippingChildren(*m_start.container());
+    return startPosition().toOffsetInAnchor().nodeAsRangeFirstNode();

[sof, 2015/05/05 08:23:23]

Is this a meaning-preserving transformation - what if the start node doesn't
have an anchor?

All uses of Range::firstNode() currently crash as a result - addressing via
https://codereview.chromium.org/1121633004/

 }
 
 ShadowRoot* Range::shadowRoot() const
 {
     return startContainer() ? startContainer()->containingShadowRoot() : nullptr;
 }
 
 Node* Range::pastLastNode() const
 {
-    if (m_end.container()->offsetInCharacters())
-        return NodeTraversal::nextSkippingChildren(*m_end.container());
-    if (Node* child = NodeTraversal::childAt(*m_end.container(), m_end.offset()))
-        return child;
-    return NodeTraversal::nextSkippingChildren(*m_end.container());
+    return endPosition().toOffsetInAnchor().nodeAsRangePastLastNode();
 }
 
 IntRect Range::boundingBox() const
 {
     IntRect result;
     Vector<IntRect> rects;
     textRects(rects);
     for (const IntRect& rect : rects)
         result.unite(rect);
     return result;
@@ skipping 357 matching lines @@
 
 void showTree(const blink::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