Clear TemplateContentDocumentFragment::m_host when HTMLTemplateElement is destroyed

Source/core/html/HTMLTemplateElement.h

 /*
  * Copyright (c) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef HTMLTemplateElement_h
 #define HTMLTemplateElement_h
 
-#include "core/dom/DocumentFragment.h"
 #include "core/html/HTMLElement.h"
 
 namespace WebCore {
 
+class DocumentFragment;
+class TemplateContentDocumentFragment;
+
 class HTMLTemplateElement FINAL : public HTMLElement {
 public:
     static PassRefPtr<HTMLTemplateElement> create(const QualifiedName&, Document&);
     virtual ~HTMLTemplateElement();
 
     DocumentFragment* content() const;
 
 private:
     virtual PassRefPtr<Node> cloneNode(bool deep = true) OVERRIDE;
     virtual void didMoveToNewDocument(Document* oldDocument) OVERRIDE;
 
     HTMLTemplateElement(const QualifiedName&, Document&);
 
-    mutable RefPtr<DocumentFragment> m_content;
+    mutable RefPtr<TemplateContentDocumentFragment> m_content;
 };
 
 inline HTMLTemplateElement* toHTMLTemplateElement(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || (node->isHTMLElement() && node->hasTagName(HTMLNames::templateTag)));
     return static_cast<HTMLTemplateElement*>(node);
 }
 
 inline const HTMLTemplateElement* toHTMLTemplateElement(const Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || (node->isHTMLElement() && node->hasTagName(HTMLNames::templateTag)));
     return static_cast<const HTMLTemplateElement*>(node);
 }
 
 } // namespace WebCore
 
 #endif // HTMLTemplateElement_h