Use the two Custom Elements node bits to explicitly represent four states.

Source/core/dom/Node.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 2663 matching lines @@
     ASSERT(isUserActionElement());
     return document()->userActionElements().isHovered(this);
 }
 
 bool Node::isUserActionElementFocused() const
 {
     ASSERT(isUserActionElement());
     return document()->userActionElements().isFocused(this);
 }
 
-void Node::setIsCustomElement()
+void Node::setCustomElementState(CustomElementState newState)
 {
+    CustomElementState oldState = customElementState();
+
+    switch (newState) {
+    case NotCustomElement:
+        ASSERT_NOT_REACHED(); // Everything starts in this state
+        return;
+
+    case UpgradeCandidate:
+        ASSERT(NotCustomElement == oldState);
+        break;
+
+    case Defined:
+        ASSERT(UpgradeCandidate == oldState || NotCustomElement == oldState);
+        break;
+
+    case Upgraded:
+        ASSERT(Defined == oldState);
+        break;
+    }
+
     ASSERT(isHTMLElement() || isSVGElement());
-    setFlag(IsCustomElement);
-}
+    setFlag(newState & 1, CustomElementBit0);
+    setFlag(newState & 2, CustomElementBit1);
 
-void Node::setIsUpgradedCustomElement()
-{
-    ASSERT(isCustomElement());
-    setFlag(IsUpgradedCustomElement);
-    setNeedsStyleRecalc(); // :unresolved has changed
+    if (oldState == NotCustomElement || newState == Upgraded)
+        setNeedsStyleRecalc(); // :unresolved has changed
 }
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 
 void showTree(const WebCore::Node* node)
 {
     if (node)
         node->showTreeForThis();
 }
 
 void showNodePath(const WebCore::Node* node)
 {
     if (node)
         node->showNodePathForThis();
 }
 
 #endif