We should unify various forms of tree traversal in DOM

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index 7465bdd137d45a83afa4d6274d056a4c3cbfb9a6..0fab26e36c229642e40cbb5796a7fa86bf371fab 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -171,6 +171,9 @@ public:
     virtual String nodeValue() const;
     virtual void setNodeValue(const String&);
     virtual NodeType nodeType() const = 0;
+    // FIXME: We should get rid of parentNode() usage and replace with parent()

[eseidel, 2014/01/07 19:14:00]

parentNode is part of the DOM API.  But we can prefer parent() internally if we
like.

+    // to bring us inline with the API of other tree structures in the codebase.
+    ContainerNode* parent() const { return parentNode(); }

[esprehn, 2014/01/07 19:16:37]

Not really a fan of this, I don't think we should start using parent instead of
parentNode, diverging from the JS API just makes things confusing.

     ContainerNode* parentNode() const;
     Element* parentElement() const;
     Node* previousSibling() const { return m_previous; }