Teach V8GCController how to traverse TemplateContentDocumentFragment::host

Source/core/dom/TemplateContentDocumentFragment.h

Index: Source/core/dom/TemplateContentDocumentFragment.h
diff --git a/Source/core/dom/TemplateContentDocumentFragment.h b/Source/core/dom/TemplateContentDocumentFragment.h
index 6c44e6075eea706843dffeacce91ecec4a06951d..380e8fa48b25250083dfe50185627aaeba1a4b20 100644
--- a/Source/core/dom/TemplateContentDocumentFragment.h
+++ b/Source/core/dom/TemplateContentDocumentFragment.h
@@ -33,16 +33,16 @@ namespace WebCore {
 
 class TemplateContentDocumentFragment FINAL : public DocumentFragment {
 public:
-    static PassRefPtr<TemplateContentDocumentFragment> create(Document& document, const Element* host)
+    static PassRefPtr<TemplateContentDocumentFragment> create(Document& document, Element* host)
     {
         return adoptRef(new TemplateContentDocumentFragment(document, host));
     }
 
-    const Element* host() const { return m_host; }
+    Element* host() const { return m_host; }
     void clearHost() { m_host = 0; }
 
 private:
-    TemplateContentDocumentFragment(Document& document, const Element* host)
+    TemplateContentDocumentFragment(Document& document, Element* host)
         : DocumentFragment(&document, CreateDocumentFragment)
         , m_host(host)
     {
@@ -50,7 +50,7 @@ private:
 
     virtual bool isTemplateContent() const OVERRIDE { return true; }
 
-    const Element* m_host;
+    Element* m_host;
 };
 
 } // namespace WebCore