Oilpan: Prepare to move RenderObject and RenderObjectChildList to Oilpan heap.

Source/core/rendering/RenderListMarker.cpp

Index: Source/core/rendering/RenderListMarker.cpp
diff --git a/Source/core/rendering/RenderListMarker.cpp b/Source/core/rendering/RenderListMarker.cpp
index f85d81e9ac806c01ab329f03f374215ae09f9d43..b127c8cebc262accbd4c618eb8d1140c2d8b8567 100644
--- a/Source/core/rendering/RenderListMarker.cpp
+++ b/Source/core/rendering/RenderListMarker.cpp
@@ -1067,6 +1067,12 @@ RenderListMarker::~RenderListMarker()
         m_image->removeClient(this);
 }
 
+void RenderListMarker::trace(Visitor* visitor)
+{
+    visitor->trace(m_listItem);
+    RenderBox::trace(visitor);
+}
+
 RenderListMarker* RenderListMarker::createAnonymous(RenderListItem* item)
 {
     Document& document = item->document();