[Oilpan]: Make StylePropertySet fully garbage collected.

Source/core/dom/ElementDataCache.h

Index: Source/core/dom/ElementDataCache.h
diff --git a/Source/core/dom/ElementDataCache.h b/Source/core/dom/ElementDataCache.h
index f1ff1b93b3a3c73dae05c44470c3e0dbd20672f2..912279e77cc8c8b39a5e0dce96b6c1464fb49e8f 100644
--- a/Source/core/dom/ElementDataCache.h
+++ b/Source/core/dom/ElementDataCache.h
@@ -27,6 +27,7 @@
 #ifndef ElementDataCache_h
 #define ElementDataCache_h
 
+#include "platform/heap/Handle.h"
 #include "wtf/HashMap.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/PassRefPtr.h"
@@ -44,12 +45,12 @@ public:
     static PassOwnPtr<ElementDataCache> create() { return adoptPtr(new ElementDataCache); }
     ~ElementDataCache();
 
-    PassRefPtr<ShareableElementData> cachedShareableElementDataWithAttributes(const Vector<Attribute>&);
+    PassRefPtrWillBeRawPtr<ShareableElementData> cachedShareableElementDataWithAttributes(const Vector<Attribute>&);
 
 private:
     ElementDataCache();
 
-    typedef HashMap<unsigned, RefPtr<ShareableElementData>, AlreadyHashed> ShareableElementDataCache;
+    typedef WillBePersistentHeapHashMap<unsigned, RefPtrWillBeMember<ShareableElementData>, AlreadyHashed> ShareableElementDataCache;
     ShareableElementDataCache m_shareableElementDataCache;
 };