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

Source/core/rendering/RenderListItem.cpp

Index: Source/core/rendering/RenderListItem.cpp
diff --git a/Source/core/rendering/RenderListItem.cpp b/Source/core/rendering/RenderListItem.cpp
index 51b891ebec9229f76320d8dd8af340ef1ff68fa8..6c251c4263ad53e95a8804e375c1e8ec97d2d89d 100644
--- a/Source/core/rendering/RenderListItem.cpp
+++ b/Source/core/rendering/RenderListItem.cpp
@@ -39,7 +39,7 @@ using namespace HTMLNames;
 
 RenderListItem::RenderListItem(Element* element)
     : RenderBlockFlow(element)
-    , m_marker(0)
+    , m_marker(nullptr)
     , m_hasExplicitValue(false)
     , m_isValueUpToDate(false)
     , m_notInList(false)
@@ -47,6 +47,12 @@ RenderListItem::RenderListItem(Element* element)
     setInline(false);
 }
 
+void RenderListItem::trace(Visitor* visitor)
+{
+    visitor->trace(m_marker);
+    RenderBlockFlow::trace(visitor);
+}
+
 void RenderListItem::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
 {
     RenderBlockFlow::styleDidChange(diff, oldStyle);
@@ -62,7 +68,7 @@ void RenderListItem::styleDidChange(StyleDifference diff, const RenderStyle* old
         m_marker->setStyle(newStyle.release());
     } else if (m_marker) {
         m_marker->destroy();
-        m_marker = 0;
+        m_marker = nullptr;
     }
 }
 
@@ -70,7 +76,7 @@ void RenderListItem::willBeDestroyed()
 {
     if (m_marker) {
         m_marker->destroy();
-        m_marker = 0;
+        m_marker = nullptr;
     }
     RenderBlockFlow::willBeDestroyed();
 }