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 c1e3cb587f8702f4ba068ba2105f3a26d535526f..d036ed0090909f7310075eb356b000a2b416afb2 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -171,6 +171,7 @@ public:
     virtual String nodeValue() const;
     virtual void setNodeValue(const String&);
     virtual NodeType nodeType() const = 0;
+    ContainerNode* parent() const { return parentNode(); }

[Inactive, 2014/01/07 14:37:03]

Longer term, we probably want to get rid of parentNode() and use
ImplementedAs=parent in Node.idl. parentNode() is used quite a lot of native
side also so this would be a big but mechanical change.

Maybe add a FIXME if others agree?

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