Move Node/ContainerNode's traverseToChildAt() to NodeTraversal

Source/core/editing/InsertParagraphSeparatorCommand.cpp

Index: Source/core/editing/InsertParagraphSeparatorCommand.cpp
diff --git a/Source/core/editing/InsertParagraphSeparatorCommand.cpp b/Source/core/editing/InsertParagraphSeparatorCommand.cpp
index c9efdc6744f370f9f9c41ca6376dc4aa7697e7bd..769b533e80420d19fb7d16ac5f857bad0e543b31 100644
--- a/Source/core/editing/InsertParagraphSeparatorCommand.cpp
+++ b/Source/core/editing/InsertParagraphSeparatorCommand.cpp
@@ -283,7 +283,7 @@ void InsertParagraphSeparatorCommand::doApply()
             refNode = startBlock->firstChild();
         }
         else if (insertionPosition.deprecatedNode() == startBlock && nestNewBlock) {
-            refNode = startBlock->traverseToChildAt(insertionPosition.deprecatedEditingOffset());
+            refNode = NodeTraversal::childAt(*startBlock, insertionPosition.deprecatedEditingOffset());
             ASSERT(refNode); // must be true or we'd be in the end of block case
         } else
             refNode = insertionPosition.deprecatedNode();