Make sure the rootNode of a LiveNodeListBase is always a ContainerNode

Source/core/html/HTMLCollection.h

Index: Source/core/html/HTMLCollection.h
diff --git a/Source/core/html/HTMLCollection.h b/Source/core/html/HTMLCollection.h
index ce6505a4fe04a16be3a6f583f792b511a2ccb29d..06d3af4687b6bf5b99d6b5dc090fea12eef3b120 100644
--- a/Source/core/html/HTMLCollection.h
+++ b/Source/core/html/HTMLCollection.h
@@ -33,7 +33,7 @@ namespace WebCore {
 
 class HTMLCollection : public ScriptWrappable, public RefCounted<HTMLCollection>, public LiveNodeListBase {
 public:
-    static PassRefPtr<HTMLCollection> create(Node* base, CollectionType);
+    static PassRefPtr<HTMLCollection> create(ContainerNode* base, CollectionType);
     virtual ~HTMLCollection();
     virtual void invalidateCache() const OVERRIDE;
 
@@ -62,10 +62,10 @@ public:
     virtual Element* virtualItemAfter(Element*) const;
 
     Element* traverseToFirstElement(ContainerNode& root) const;
-    Element* traverseForwardToOffset(unsigned offset, Element& currentElement, unsigned& currentOffset, ContainerNode* root) const;
+    Element* traverseForwardToOffset(unsigned offset, Element& currentElement, unsigned& currentOffset, ContainerNode& root) const;
 
 protected:
-    HTMLCollection(Node* base, CollectionType, ItemAfterOverrideType);
+    HTMLCollection(ContainerNode* base, CollectionType, ItemAfterOverrideType);
 
     virtual void updateNameCache() const;
     bool hasNameCache() const { return m_isNameCacheValid; }
@@ -79,7 +79,7 @@ protected:
 
 private:
     bool checkForNameMatch(Element*, bool checkName, const AtomicString& name) const;
-    Element* traverseNextElement(Element& previous, ContainerNode* root) const;
+    Element* traverseNextElement(Element& previous, ContainerNode& root) const;
 
     static void append(NodeCacheMap&, const AtomicString&, Element*);
     void invalidateIdNameCacheMaps() const