Move LayoutObject to satellite NodeLayoutData that hangs from a Node.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004-2011, 2014 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 79 matching lines @@
   kFailed = 3 << kNodeCustomElementShift,
 
   kNotDefinedFlag = 2 << kNodeCustomElementShift,
 };
 
 enum class SlotChangeType {
   kInitial,
   kChained,
 };
 
-class NodeRareDataBase {
+class NodeLayoutData {
  public:
+  explicit NodeLayoutData(LayoutObject* layout_object) : layout_object_(layout_object) {}
   LayoutObject* GetLayoutObject() const { return layout_object_; }
   void SetLayoutObject(LayoutObject* layout_object) {
     layout_object_ = layout_object;
   }
 
- protected:
-  NodeRareDataBase(LayoutObject* layout_object)
-      : layout_object_(layout_object) {}
+ private:
+  LayoutObject* layout_object_;
+};
 
- protected:
-  // LayoutObjects are fully owned by their DOM node. See LayoutObject's
-  // LIFETIME documentation section.
-  LayoutObject* layout_object_;
+class NodeRareDataBase {
 };
 
 class Node;
 WILL_NOT_BE_EAGERLY_TRACED_CLASS(Node);
 
 // This class represents a DOM node in the DOM tree.
 // https://dom.spec.whatwg.org/#interface-node
 class CORE_EXPORT Node : public EventTarget {
   DEFINE_WRAPPERTYPEINFO();
   friend class TreeScope;
@@ skipping 431 matching lines @@
   virtual bool CanStartSelection() const;
 
   // -----------------------------------------------------------------------------
   // Integration with layout tree
 
   // As layoutObject() includes a branch you should avoid calling it repeatedly
   // in hot code paths.
   // Note that if a Node has a layoutObject, it's parentNode is guaranteed to
   // have one as well.
   LayoutObject* GetLayoutObject() const {
-    return HasRareData() ? data_.rare_data_->GetLayoutObject()
-                         : data_.layout_object_;
+    return data_.node_layout_data_ ? data_.node_layout_data_->GetLayoutObject() : nullptr;
   }
   void SetLayoutObject(LayoutObject* layout_object) {
-    if (HasRareData())
-      data_.rare_data_->SetLayoutObject(layout_object);
-    else
-      data_.layout_object_ = layout_object;
+    data_.node_layout_data_->SetLayoutObject(layout_object);
   }
 
   // Use these two methods with caution.
   LayoutBox* GetLayoutBox() const;
   LayoutBoxModelObject* GetLayoutBoxModelObject() const;
 
   struct AttachContext {
     STACK_ALLOCATED();
     ComputedStyle* resolved_style = nullptr;
     bool performing_reattach = false;
@@ skipping 334 matching lines @@
   const HeapHashSet<TraceWrapperMember<MutationObserverRegistration>>*
   TransientMutationObserverRegistry();
 
   uint32_t node_flags_;
   Member<ContainerNode> parent_or_shadow_host_node_;
   Member<TreeScope> tree_scope_;
   Member<Node> previous_;
   Member<Node> next_;
   // When a node has rare data we move the layoutObject into the rare data.
   union DataUnion {
-    DataUnion() : layout_object_(nullptr) {}
+    DataUnion() : node_layout_data_(nullptr) {}
     // LayoutObjects are fully owned by their DOM node. See LayoutObject's
     // LIFETIME documentation section.
-    LayoutObject* layout_object_;
+    NodeLayoutData* node_layout_data_;

[nainar, 2017/04/11 06:03:59]

If the DataUnion is a NodeLayoutData we then have a LayoutObject stored on the
Node through this NodeLayoutData

     NodeRareDataBase* rare_data_;

[nainar, 2017/04/11 06:03:59]

However, if we have a NodeRareDataBase we don't have a LayoutObject? 

This seems wrong. 

I think we will have to retain storing the LayoutObject on NodeRareDataBase. 

Either directly or via an instance of NodeLayoutData.

   } data_;
 };
 
 inline void Node::SetParentOrShadowHostNode(ContainerNode* parent) {
   DCHECK(IsMainThread());
   parent_or_shadow_host_node_ = parent;
   ScriptWrappableVisitor::WriteBarrier(
       this, reinterpret_cast<Node*>(parent_or_shadow_host_node_.Get()));
 }
 
@@ skipping 51 matching lines @@
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showNode(const blink::Node*);
 void showTree(const blink::Node*);
 void showNodePath(const blink::Node*);
 #endif
 
 #endif  // Node_h