Move Node/ContainerNode's traverseToChildAt() to NodeTraversal

Source/core/editing/BreakBlockquoteCommand.cpp

Index: Source/core/editing/BreakBlockquoteCommand.cpp
diff --git a/Source/core/editing/BreakBlockquoteCommand.cpp b/Source/core/editing/BreakBlockquoteCommand.cpp
index 8caf333487ffb7fe3adca3341fbe5e8d069d38fb..cfebe0501651d52849a77c036a66c26bca45cb23 100644
--- a/Source/core/editing/BreakBlockquoteCommand.cpp
+++ b/Source/core/editing/BreakBlockquoteCommand.cpp
@@ -118,7 +118,7 @@ void BreakBlockquoteCommand::doApply()
         } else if (pos.deprecatedEditingOffset() > 0)
             splitTextNode(textNode, pos.deprecatedEditingOffset());
     } else if (pos.deprecatedEditingOffset() > 0) {
-        Node* childAtOffset = startNode->traverseToChildAt(pos.deprecatedEditingOffset());
+        Node* childAtOffset = NodeTraversal::childAt(*startNode, pos.deprecatedEditingOffset());
         startNode = childAtOffset ? childAtOffset : NodeTraversal::next(*startNode);
         ASSERT(startNode);
     }