Some speculation about making opaque root finding cheaper.

third_party/WebKit/Source/core/dom/Node.h

Index: third_party/WebKit/Source/core/dom/Node.h
diff --git a/third_party/WebKit/Source/core/dom/Node.h b/third_party/WebKit/Source/core/dom/Node.h
index 14569362b0753e5e501033b88e80017145519c2a..f251527d92de4ecc0a08c5d80ef4e340618a87ea 100644
--- a/third_party/WebKit/Source/core/dom/Node.h
+++ b/third_party/WebKit/Source/core/dom/Node.h
@@ -333,7 +333,13 @@ class CORE_EXPORT Node : public EventTarget {
   void setParentOrShadowHostNode(ContainerNode*);
 
   // Knows about all kinds of hosts.
-  ContainerNode* parentOrShadowHostOrTemplateHostNode() const;
+  ContainerNode* parentOrShadowHostOrTemplateHostNode() const {
+    if (UNLIKELY(isDocumentFragment() && !isShadowRoot()))
+      return parentOrShadowHostOrTemplateHostNodeForDocumentFragment();
+    return parentOrShadowHostNode();
+  }
+  ContainerNode* parentOrShadowHostOrTemplateHostNodeForDocumentFragment()
+      const;
 
   // Returns the parent node, but nullptr if the parent node is a ShadowRoot.
   ContainerNode* nonShadowBoundaryParentNode() const;