Oilpan: move LiveNodeList collections to the heap.

Source/core/dom/NodeRareData.cpp

Index: Source/core/dom/NodeRareData.cpp
diff --git a/Source/core/dom/NodeRareData.cpp b/Source/core/dom/NodeRareData.cpp
index c29894c2a00a5f2807675c7d17679ae65a955043..a347406ea4fee114bd1888840e92a84bd99935df 100644
--- a/Source/core/dom/NodeRareData.cpp
+++ b/Source/core/dom/NodeRareData.cpp
@@ -58,9 +58,33 @@ void NodeListsNodeData::invalidateCaches(const QualifiedName* attrName)
         it->value->invalidateCache();
 }
 
+#if ENABLE(OILPAN)
+void NodeListsNodeData::clearWeakMembers(Visitor* visitor)
+{
+    if (m_childNodeList && !visitor->isAlive(m_childNodeList))

[haraken, 2014/05/20 09:27:33]

Nit: You don't need to check m_childNodeList.

+        m_childNodeList.clear();
+    if (!m_childNodeList && !m_atomicNameCaches.size() && !m_tagCollectionCacheNS.size())
+        m_owner->clearNodeLists();
+}
+#endif
+
+void NodeListsNodeData::trace(Visitor* visitor)
+{
+#if ENABLE(OILPAN)

[Erik Corry, 2014/05/20 09:09:48]

An alternative (I think simpler) way to do this would be to just have
m_childNodeList be a weak pointer and call trace on in normally.  In the trace
method of the NodeRareData you check whether the NodeListsNodeData is empty and
if it is you zero the pointer instead of tracing it.  This way there are no
explicitly registered weak callbacks.  The NodeListsNodeData is deleted one GC
later than the rest, but I don't think that's a big deal.

[sof, 2014/05/20 09:54:57]

I like this,it just fits better all around to move the is-empty checking out of
NodeListsNodeData to the object holding the reference. Done.

+    visitor->trace(m_atomicNameCaches);
+    visitor->trace(m_tagCollectionCacheNS);
+    visitor->trace(m_owner);
+    // NOTE: The m_childNodeList weak member is manually updated in
+    // clearWeakMembers() above hence not traced as a weak member
+    // here.
+    visitor->registerWeakMembers<NodeListsNodeData, &NodeListsNodeData::clearWeakMembers>(this);
+#endif
+}
+
 void NodeRareData::traceAfterDispatch(Visitor* visitor)
 {
     visitor->trace(m_mutationObserverData);
+    visitor->trace(m_nodeLists);
 }
 
 void NodeRareData::trace(Visitor* visitor)