add 'slow' prefix to RenderObject's firstChild() / lastChild() methods

Source/core/dom/Position.cpp

Index: Source/core/dom/Position.cpp
diff --git a/Source/core/dom/Position.cpp b/Source/core/dom/Position.cpp
index 6e98a73bdb4a1352ce8b411f9b4081cd6d0df433..64f8730cc6f540937921deecae0cba42dc7c9d30 100644
--- a/Source/core/dom/Position.cpp
+++ b/Source/core/dom/Position.cpp
@@ -804,7 +804,7 @@ static int boundingBoxLogicalHeight(RenderObject *o, const IntRect &rect)
 bool Position::hasRenderedNonAnonymousDescendantsWithHeight(RenderObject* renderer)
 {
     RenderObject* stop = renderer->nextInPreOrderAfterChildren();
-    for (RenderObject *o = renderer->firstChild(); o && o != stop; o = o->nextInPreOrder())
+    for (RenderObject *o = renderer->slowFirstChild(); o && o != stop; o = o->nextInPreOrder())
         if (o->nonPseudoNode()) {
             if ((o->isText() && boundingBoxLogicalHeight(o, toRenderText(o)->linesBoundingBox()))
                 || (o->isBox() && toRenderBox(o)->pixelSnappedLogicalHeight())
@@ -1067,7 +1067,7 @@ void Position::getInlineBoxAndOffset(EAffinity affinity, InlineBox*& inlineBox,
 
 static bool isNonTextLeafChild(RenderObject* object)
 {
-    if (object->firstChild())
+    if (object->slowFirstChild())
         return false;
     if (object->isText())
         return false;