Do not allocate SlotAssignment unless a shadowroot has a slot

third_party/WebKit/Source/core/dom/shadow/ShadowRoot.h

 /*
  * Copyright (C) 2011 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 105 matching lines @@
   const HeapVector<Member<InsertionPoint>>& descendantInsertionPoints();
 
   // For Internals, don't use this.
   unsigned childShadowRootCount() const { return m_childShadowRootCount; }
 
   void recalcStyle(StyleRecalcChange);
 
   void registerScopedHTMLStyleChild();
   void unregisterScopedHTMLStyleChild();
 
-  SlotAssignment& ensureSlotAssignment();
+  SlotAssignment& slotAssignment() {
+    DCHECK(m_slotAssignment);
+    return *m_slotAssignment;
+  }
+
+  HTMLSlotElement* assignedSlotFor(const Node&);
+  void didAddSlot(HTMLSlotElement&);
+  void didChangeHostChildSlotName(const AtomicString& oldValue,
+                                  const AtomicString& newValue);
 
   void distributeV1();
 
   Element* activeElement() const;
 
   String innerHTML() const;
   void setInnerHTML(const String&, ExceptionState& = ASSERT_NO_EXCEPTION);
 
   Node* cloneNode(bool, ExceptionState&);
 
@@ skipping 11 matching lines @@
   DECLARE_VIRTUAL_TRACE();
   DECLARE_VIRTUAL_TRACE_WRAPPERS();
 
  private:
   ShadowRoot(Document&, ShadowRootType);
   ~ShadowRoot() override;
 
   void childrenChanged(const ChildrenChange&) override;
 
   ShadowRootRareDataV0& ensureShadowRootRareDataV0();
+  SlotAssignment& ensureSlotAssignment();
 
   void addChildShadowRoot() { ++m_childShadowRootCount; }
   void removeChildShadowRoot() {
     DCHECK_GT(m_childShadowRootCount, 0u);
     --m_childShadowRootCount;
   }
   void invalidateDescendantInsertionPoints();
 
   // ShadowRoots should never be cloned.
   Node* cloneNode(bool) override { return nullptr; }
@@ skipping 25 matching lines @@
                   treeScope,
                   treeScope->rootNode().isShadowRoot(),
                   treeScope.rootNode().isShadowRoot());
 DEFINE_TYPE_CASTS(TreeScope, ShadowRoot, shadowRoot, true, true);
 
 CORE_EXPORT std::ostream& operator<<(std::ostream&, const ShadowRootType&);
 
 }  // namespace blink
 
 #endif  // ShadowRoot_h