Only allow one shadowRoot.

sky/engine/core/dom/Element.h

Index: sky/engine/core/dom/Element.h
diff --git a/sky/engine/core/dom/Element.h b/sky/engine/core/dom/Element.h
index 432a886b00d2773d0b784ed96fe7a500529810eb..4f5a234c1a13f153fd368509f777d5e275f99138 100644
--- a/sky/engine/core/dom/Element.h
+++ b/sky/engine/core/dom/Element.h
@@ -209,9 +209,8 @@ public:
 
     ElementShadow* shadow() const;
     ElementShadow& ensureShadow();
-    PassRefPtr<ShadowRoot> createShadowRoot(ExceptionState&);
+    PassRefPtr<ShadowRoot> ensureShadowRoot(ExceptionState&);
     ShadowRoot* shadowRoot() const;
-    ShadowRoot* youngestShadowRoot() const;
 
     bool hasAuthorShadowRoot() const { return shadowRoot(); }
 
@@ -547,6 +546,13 @@ inline void Node::removedFrom(ContainerNode* insertionPoint)
         clearFlag(IsInShadowTreeFlag);
 }
 
+inline ShadowRoot* Node::shadowRoot() const
+{
+    if (!isElementNode())
+        return 0;
+    return toElement(this)->shadowRoot();
+}
+
 inline void Element::invalidateStyleAttribute()
 {
     ASSERT(elementData());