Process Custom Elements in post-order.

Source/core/dom/CustomElement.h

Index: Source/core/dom/CustomElement.h
diff --git a/Source/core/dom/CustomElement.h b/Source/core/dom/CustomElement.h
index 4fc4b572ae85c4135a532727db0a28cc037ba276..205c04edce49c3238c75b1d679542c52d44a9eb9 100644
--- a/Source/core/dom/CustomElement.h
+++ b/Source/core/dom/CustomElement.h
@@ -33,6 +33,7 @@
 
 #include "core/dom/CustomElementDefinition.h"
 #include "wtf/HashMap.h"
+#include "wtf/HashSet.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
@@ -55,6 +56,7 @@ public:
     static void allowTagName(const AtomicString& localName);
 
     // API for registration contexts
+    static void setBeingParsed(Element*);
     static void define(Element*, PassRefPtr<CustomElementDefinition>);
 
     // API for wrapper creation, which uses a definition as a key
@@ -62,6 +64,7 @@ public:
 
     // API for Element to kick off changes
 
+    static void finishedParsingChildren(Element*);
     static void attributeDidChange(Element*, const AtomicString& name, const AtomicString& oldValue, const AtomicString& newValue);
     static void didEnterDocument(Element*, Document*);
     static void didLeaveDocument(Element*, Document*);
@@ -89,6 +92,10 @@ private:
         ElementDefinitionHashMap m_definitions;
     };
     static DefinitionMap& definitions();
+
+    typedef HashSet<Element*> ElementSet;
+    static ElementSet& elementsBeingParsed();
+    static void setFinishedParsing(Element*);
 };
 
 }