Make sure the rootNode of a LiveNodeListBase is always a ContainerNode

Source/core/html/LabelsNodeList.h

Index: Source/core/html/LabelsNodeList.h
diff --git a/Source/core/html/LabelsNodeList.h b/Source/core/html/LabelsNodeList.h
index 35f36c3ecefec83f17f207f8dc80bc9210fa88b1..2985fac3ab692794ac0c9e79285f1fe5c8428c78 100644
--- a/Source/core/html/LabelsNodeList.h
+++ b/Source/core/html/LabelsNodeList.h
@@ -32,7 +32,7 @@ namespace WebCore {
 
 class LabelsNodeList FINAL : public LiveNodeList {
 public:
-    static PassRefPtr<LabelsNodeList> create(Node* ownerNode, CollectionType type, const AtomicString&)
+    static PassRefPtr<LabelsNodeList> create(ContainerNode* ownerNode, CollectionType type, const AtomicString&)
     {
         ASSERT_UNUSED(type, type == LabelsNodeListType);
         return adoptRef(new LabelsNodeList(ownerNode));
@@ -41,7 +41,7 @@ public:
     virtual ~LabelsNodeList();
 
 protected:
-    explicit LabelsNodeList(Node*);
+    explicit LabelsNodeList(ContainerNode*);
 
     virtual bool nodeMatches(Element*) const OVERRIDE;
 };