Make IDL Callbacks non-refcounted by default

Source/core/dom/MutationObserver.h

Index: Source/core/dom/MutationObserver.h
diff --git a/Source/core/dom/MutationObserver.h b/Source/core/dom/MutationObserver.h
index ff3c442524b1cede8e66b3fa939f38e1943095e3..062d01edfe13534de67bb59365f1393c5a2cbbf6 100644
--- a/Source/core/dom/MutationObserver.h
+++ b/Source/core/dom/MutationObserver.h
@@ -70,7 +70,7 @@ public:
         CharacterDataOldValue = 1 << 6,
     };
 
-    static PassRefPtr<MutationObserver> create(PassRefPtr<MutationCallback>);
+    static PassRefPtr<MutationObserver> create(PassOwnPtr<MutationCallback>);
     static void deliverAllMutations();
 
     ~MutationObserver();
@@ -89,10 +89,10 @@ public:
 private:
     struct ObserverLessThan;
 
-    explicit MutationObserver(PassRefPtr<MutationCallback>);
+    explicit MutationObserver(PassOwnPtr<MutationCallback>);
     void deliver();
 
-    RefPtr<MutationCallback> m_callback;
+    OwnPtr<MutationCallback> m_callback;
     Vector<RefPtr<MutationRecord> > m_records;
     HashSet<MutationObserverRegistration*> m_registrations;
     unsigned m_priority;