WIP (Introduce WTF::NonNullPtr<T>.)

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index 25c434b6a8e8bbde4f104467b4a499e5d6d57246..b6e773934fb7e73013a637a32fabde4d36325313 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -724,9 +724,9 @@ private:
     void synchronizeAttribute(const AtomicString& localName) const;
 
     void updateId(const AtomicString& oldId, const AtomicString& newId);
-    void updateId(TreeScope&, const AtomicString& oldId, const AtomicString& newId);
+    void updateId(NonNullPtr<TreeScope>, const AtomicString& oldId, const AtomicString& newId);
     void updateName(const AtomicString& oldName, const AtomicString& newName);
-    void updateLabel(TreeScope&, const AtomicString& oldForAttributeValue, const AtomicString& newForAttributeValue);
+    void updateLabel(NonNullPtr<TreeScope>, const AtomicString& oldForAttributeValue, const AtomicString& newForAttributeValue);
 
     void scrollByUnits(int units, ScrollGranularity);
 
@@ -986,7 +986,7 @@ inline void Node::removedFrom(ContainerNode* insertionPoint)
     ASSERT(insertionPoint->inDocument() || isContainerNode());
     if (insertionPoint->inDocument())
         clearFlag(InDocumentFlag);
-    if (isInShadowTree() && !treeScope().rootNode()->isShadowRoot())
+    if (isInShadowTree() && !treeScope()->rootNode()->isShadowRoot())
         clearFlag(IsInShadowTreeFlag);
 }