Oilpan: move HistoryItem to the heap.

Source/core/loader/FrameLoader.h

Index: Source/core/loader/FrameLoader.h
diff --git a/Source/core/loader/FrameLoader.h b/Source/core/loader/FrameLoader.h
index 54710989cc92ab8514925d4d78b3bd22e1c6743d..f5d03c941d885dcafbc53401743f92af92403ff2 100644
--- a/Source/core/loader/FrameLoader.h
+++ b/Source/core/loader/FrameLoader.h
@@ -239,9 +239,12 @@ private:
     RefPtr<DocumentLoader> m_policyDocumentLoader;
     OwnPtrWillBeMember<FetchContext> m_fetchContext;
 
-    RefPtr<HistoryItem> m_currentItem;
-    RefPtr<HistoryItem> m_provisionalItem;
+    RefPtrWillBeMember<HistoryItem> m_currentItem;
+    RefPtrWillBeMember<HistoryItem> m_provisionalItem;
+
     struct DeferredHistoryLoad {
+        DISALLOW_ALLOCATION();
+    public:
         DeferredHistoryLoad(HistoryItem* item, HistoryLoadType type, ResourceRequestCachePolicy cachePolicy)
             : m_item(item)
             , m_type(type)
@@ -253,10 +256,16 @@ private:
 
         bool isValid() { return m_item; }
 
-        RefPtr<HistoryItem> m_item;
+        void trace(Visitor* visitor)
+        {
+            visitor->trace(m_item);
+        }
+
+        RefPtrWillBeMember<HistoryItem> m_item;
         HistoryLoadType m_type;
         ResourceRequestCachePolicy m_cachePolicy;
     };
+
     DeferredHistoryLoad m_deferredHistoryLoad;
 
     bool m_inStopAllLoaders;