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

Source/core/rendering/RenderObjectChildList.h

Index: Source/core/rendering/RenderObjectChildList.h
diff --git a/Source/core/rendering/RenderObjectChildList.h b/Source/core/rendering/RenderObjectChildList.h
index 7b5c57a06c63b5b8e4e84f1eab8257fa1cf848f5..da4575b13a60db8f4c5dcdbf18f02074a9d59752 100644
--- a/Source/core/rendering/RenderObjectChildList.h
+++ b/Source/core/rendering/RenderObjectChildList.h
@@ -26,6 +26,7 @@
 #ifndef RenderObjectChildList_h
 #define RenderObjectChildList_h
 
+#include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
 
 namespace blink {
@@ -33,15 +34,17 @@ namespace blink {
 class RenderObject;
 
 class RenderObjectChildList {
+    DISALLOW_ALLOCATION();
 public:
     RenderObjectChildList()
-        : m_firstChild(0)
-        , m_lastChild(0)
+        : m_firstChild(nullptr)
+        , m_lastChild(nullptr)
     {
     }
+    void trace(Visitor*);
 
-    RenderObject* firstChild() const { return m_firstChild; }
-    RenderObject* lastChild() const { return m_lastChild; }
+    RenderObject* firstChild() const { return m_firstChild.get(); }
+    RenderObject* lastChild() const { return m_lastChild.get(); }
 
     // FIXME: Temporary while RenderBox still exists. Eventually this will just happen during insert/append/remove methods on the child list, and nobody
     // will need to manipulate firstChild or lastChild directly.
@@ -58,8 +61,8 @@ public:
     }
 
 private:
-    RenderObject* m_firstChild;
-    RenderObject* m_lastChild;
+    RawPtrWillBeMember<RenderObject> m_firstChild;
+    RawPtrWillBeMember<RenderObject> m_lastChild;
 };
 
 } // namespace blink