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

Source/core/editing/TextIterator.cpp

Index: Source/core/editing/TextIterator.cpp
diff --git a/Source/core/editing/TextIterator.cpp b/Source/core/editing/TextIterator.cpp
index 61072a597d8488a13c155bb1c842a4bc1c1961e6..c62fb7e13f968d93416ab829a008d2ebdcd67def 100644
--- a/Source/core/editing/TextIterator.cpp
+++ b/Source/core/editing/TextIterator.cpp
@@ -749,7 +749,7 @@ static inline RenderText* firstRenderTextInFirstLetter(RenderObject* firstLetter
         return 0;
 
     // FIXME: Should this check descendent objects?
-    for (RenderObject* current = firstLetter->firstChild(); current; current = current->nextSibling()) {
+    for (RenderObject* current = firstLetter->slowFirstChild(); current; current = current->nextSibling()) {
         if (current->isText())
             return toRenderText(current);
     }