Get rid of TreeBoundaryCrossingRules.

Source/core/dom/TreeScope.h

Index: Source/core/dom/TreeScope.h
diff --git a/Source/core/dom/TreeScope.h b/Source/core/dom/TreeScope.h
index 1bfcdf91861bd05cc0b548b98cc7eebc3ba2422e..9c08a3a75cc62a7568c8c31d07838cbbf20b097d 100644
--- a/Source/core/dom/TreeScope.h
+++ b/Source/core/dom/TreeScope.h
@@ -141,6 +141,10 @@ public:
     ScopedStyleResolver& ensureScopedStyleResolver();
     void clearScopedStyleResolver();
 
+    TreeScope* composedParent();
+
+    static TreeScope* treeScopeInComposedTree(const Node&);
+
 protected:
     TreeScope(ContainerNode&, Document&);
     TreeScope(Document&);
@@ -152,6 +156,7 @@ protected:
 
     void setDocument(Document& document) { m_document = &document; }
     void setParentTreeScope(TreeScope&);
+    void clearComposedParent() { m_composedParent = nullptr; }
 
 #if !ENABLE(OILPAN)
     bool hasGuardRefCount() const { return m_guardRefCount; }
@@ -179,6 +184,7 @@ private:
     RawPtrWillBeMember<ContainerNode> m_rootNode;
     RawPtrWillBeMember<Document> m_document;
     RawPtrWillBeMember<TreeScope> m_parentTreeScope;
+    RawPtrWillBeMember<TreeScope> m_composedParent;
 
 #if !ENABLE(OILPAN)
     int m_guardRefCount;