Teach V8GCController how to traverse TemplateContentDocumentFragment::host

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index 1fe0467f9e3dfae905f5854fa1b554ba67bbd627..72fe6c674ddb1efb64609f379d2e7f8196141ff5 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -291,6 +291,9 @@ public:
     void setParentOrShadowHostNode(ContainerNode*);
     Node* highestAncestor() const;
 
+    // Knows about all kinds of hosts.
+    ContainerNode* parentOrShadowHostOrTemplateHostNode() const;
+
     // Use when it's guaranteed to that shadowHost is 0.
     ContainerNode* parentNodeGuaranteedHostFree() const;
     // Returns the parent node, but 0 if the parent node is a ShadowRoot.