Make IDL Callbacks non-refcounted by default

Source/core/dom/MutationObserver.cpp

Index: Source/core/dom/MutationObserver.cpp
diff --git a/Source/core/dom/MutationObserver.cpp b/Source/core/dom/MutationObserver.cpp
index ebe56393b3a40ff6bead51ba5c6ed8eae4bf94b4..abf2278986973e5f0ea2e37f2d1aae3c4f13ba1f 100644
--- a/Source/core/dom/MutationObserver.cpp
+++ b/Source/core/dom/MutationObserver.cpp
@@ -56,13 +56,13 @@ struct MutationObserver::ObserverLessThan {
     }
 };
 
-PassRefPtr<MutationObserver> MutationObserver::create(PassRefPtr<MutationCallback> callback)
+PassRefPtr<MutationObserver> MutationObserver::create(PassOwnPtr<MutationCallback> callback)
 {
     ASSERT(isMainThread());
     return adoptRef(new MutationObserver(callback));
 }
 
-MutationObserver::MutationObserver(PassRefPtr<MutationCallback> callback)
+MutationObserver::MutationObserver(PassOwnPtr<MutationCallback> callback)
     : m_callback(callback)
     , m_priority(s_observerPriority++)
 {