Reduce a shadow root object's size by not inheriting DoublyLinkedList

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

 /*
  * Copyright (C) 2012 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 14 matching lines @@
  */
 
 #ifndef ElementShadow_h
 #define ElementShadow_h
 
 #include "core/CoreExport.h"
 #include "core/dom/shadow/InsertionPoint.h"
 #include "core/dom/shadow/SelectRuleFeatureSet.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "platform/heap/Handle.h"
-#include "wtf/DoublyLinkedList.h"
 #include "wtf/HashMap.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
 
 class CORE_EXPORT ElementShadow final : public GarbageCollectedFinalized<ElementShadow> {
     WTF_MAKE_NONCOPYABLE(ElementShadow);
 public:
     static ElementShadow* create();
     ~ElementShadow();
 
     Element* host() const;
-    ShadowRoot& youngestShadowRoot() const { DCHECK(m_shadowRoots.head()); return *m_shadowRoots.head(); }
-    ShadowRoot* oldestShadowRoot() const { return m_shadowRoots.tail(); }
+    ShadowRoot& youngestShadowRoot() const;
+    ShadowRoot* oldestShadowRoot() const { return m_shadowRoot; }
     ElementShadow* containingShadow() const;
 
     ShadowRoot& addShadowRoot(Element& shadowHost, ShadowRootType);
 
     bool hasSameStyles(const ElementShadow*) const;
 
     void attach(const Node::AttachContext&);
     void detach(const Node::AttachContext&);
 
     void willAffectSelector();
     const SelectRuleFeatureSet& ensureSelectFeatureSet();
 
     void distributeIfNeeded();
     void setNeedsDistributionRecalc();
     bool needsDistributionRecalc() const { return m_needsDistributionRecalc; }
 
     const InsertionPoint* finalDestinationInsertionPointFor(const Node*) const;
     const DestinationInsertionPoints* destinationInsertionPointsFor(const Node*) const;
 
     void didDistributeNode(const Node*, InsertionPoint*);
 
     bool isV1() const { return youngestShadowRoot().isV1(); };
     bool isOpenOrV0() const { return youngestShadowRoot().isOpenOrV0(); };
 
     DECLARE_TRACE();
 
 private:
     ElementShadow();
 
+    void appendShadowRoot(ShadowRoot&);
+
     void distribute();
     void clearDistribution();
 
     void distributeV0();
     void distributeV1();
 
     void collectSelectFeatureSetFrom(ShadowRoot&);
     void distributeNodeChildrenTo(InsertionPoint*, ContainerNode*);
 
     bool needsSelectFeatureSet() const { return m_needsSelectFeatureSet; }
     void setNeedsSelectFeatureSet() { m_needsSelectFeatureSet = true; }
 
     using NodeToDestinationInsertionPoints = HeapHashMap<Member<const Node>, Member<DestinationInsertionPoints>>;
     NodeToDestinationInsertionPoints m_nodeToInsertionPoints;
 
     SelectRuleFeatureSet m_selectFeatures;
-    // TODO(Oilpan): add a heap-based version of DoublyLinkedList<>.
-    DoublyLinkedList<ShadowRoot> m_shadowRoots;
+    Member<ShadowRoot> m_shadowRoot;
     bool m_needsDistributionRecalc;
     bool m_needsSelectFeatureSet;
 };
 
 inline Element* ElementShadow::host() const
 {
-    DCHECK(!m_shadowRoots.isEmpty());
-    return youngestShadowRoot().host();
+    DCHECK(m_shadowRoot);
+    return m_shadowRoot->host();
 }
 
 inline ShadowRoot* Node::youngestShadowRoot() const
 {
     if (!isElementNode())
         return 0;
     return toElement(this)->youngestShadowRoot();
 }
 
 inline ShadowRoot* Element::youngestShadowRoot() const
@@ skipping 13 matching lines @@
 inline void ElementShadow::distributeIfNeeded()
 {
     if (m_needsDistributionRecalc)
         distribute();
     m_needsDistributionRecalc = false;
 }
 
 } // namespace blink
 
 #endif