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 d8e9ea56c8f0fa1aa536c06afe540c64e707b276..a8a6af61db8ac74f43170ac35a5abddcd07cc15b 100644
--- a/Source/core/dom/MutationObserver.cpp
+++ b/Source/core/dom/MutationObserver.cpp
@@ -54,13 +54,13 @@ 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++)
 {