Oilpan: Switch RefCountedGarbageCollected to GarbageCollectedFinalized for Node.

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, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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
  * License as published by the Free Software Foundation; either
@@ skipping 89 matching lines @@
 
 protected:
     NodeRareDataBase(RenderObject* renderer)
         : m_renderer(renderer)
     { }
 
 private:
     RenderObject* m_renderer;
 };
 
-class Node : public EventTarget, public ScriptWrappable, public TreeSharedWillBeRefCountedGarbageCollected<Node> {
+class Node : public EventTarget, public ScriptWrappable, public TreeSharedWillBeGarbageCollectedFinalized<Node> {

[haraken, 2014/06/11 04:47:55]

GarbageCollectedFinalized should be the left-most class.

However, I'm a bit confused:

- Why was the previous code working with having RefCountedGarbageCollected at
not the left-most class?

- Why doesn't the plugin detect the error?

[haraken, 2014/06/11 04:47:55]

Ian: This is a question not related to this CL, but are we ready to replace
RefCountedGarbageCollected of classes that derive EventTarget with
GarbageCollectedFinalized?

[haraken, 2014/06/11 04:59:04]

On the other hand, I remembered that TreeShared must be the right-most class,
because we want to align TreeShared::m_refCount (32 bit interger) and
Node::m_nodeFlags (32 bit interger) into one 64 bit slot. If we put the
TreeShared at the left-most class, it will increase sizeof(Node) by 8 byte.

So you'll need to do:

// Some comment
#if ENABLE(OILPAN)
class Node : public GarbageCollectedFinalized<Node>, public EventTarget, public
ScriptWrappable {
#else
class Node : public EventTarget, public ScriptWrappable, public TreeShared<Node>
{
#endif

[Mads Ager (chromium), 2014/06/11 05:48:22]

It seems that we got lucky that the layout of the object generated by the
compiler is such that a Node pointer always points to the start of the object
even though GarbageCollectedFinalized is not inherited as the left-most base
class. We should move it around as you suggest Haraken so that we are sure that
it becomes the left-most base class.
Good question. We should update the plugin to catch this.

[Mads Ager (chromium), 2014/06/11 05:48:22]

Yes, Ian's change to move all EventTargets to the heap and use tracing instead
of ref counting for them has landed, so this is good.

[tkent, 2014/06/12 10:12:49]

Done.

     friend class Document;
     friend class TreeScope;
     friend class TreeScopeAdopter;
 
-    DEFINE_EVENT_TARGET_REFCOUNTING(TreeSharedWillBeRefCountedGarbageCollected<Node>);
+    DEFINE_EVENT_TARGET_REFCOUNTING_WILL_BE_REMOVED(TreeSharedWillBeGarbageCollectedFinalized<Node>);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(Node);
 public:
     enum NodeType {
         ELEMENT_NODE = 1,
         ATTRIBUTE_NODE = 2,
         TEXT_NODE = 3,
         CDATA_SECTION_NODE = 4,
         PROCESSING_INSTRUCTION_NODE = 7,
         COMMENT_NODE = 8,
         DOCUMENT_NODE = 9,
@@ skipping 770 matching lines @@
 // This requires isClassName(const Node&).
 #define DEFINE_NODE_TYPE_CASTS_WITH_FUNCTION(thisType) \
     template<typename T> inline thisType* to##thisType(const RefPtr<T>& node) { return to##thisType(node.get()); } \
     DEFINE_TYPE_CASTS(thisType, Node, node, is##thisType(*node), is##thisType(node))
 
 #define DECLARE_NODE_FACTORY(T) \
     static PassRefPtrWillBeRawPtr<T> create(Document&)
 #define DEFINE_NODE_FACTORY(T) \
 PassRefPtrWillBeRawPtr<T> T::create(Document& document) \
 { \
-    return adoptRefWillBeRefCountedGarbageCollected(new T(document)); \
+    return adoptRefWillBeNoop(new T(document)); \
 }
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showNode(const WebCore::Node*);
 void showTree(const WebCore::Node*);
 void showNodePath(const WebCore::Node*);
 #endif
 
 #endif