Oilpan: Replace RefPtr to Node in MutationObserver-related classes with Oilpan transition types.

Source/core/dom/MutationObserverRegistration.cpp

Index: Source/core/dom/MutationObserverRegistration.cpp
diff --git a/Source/core/dom/MutationObserverRegistration.cpp b/Source/core/dom/MutationObserverRegistration.cpp
index 0ba07f1d38a2f679fb86a9192060c2367ff9f88a..76d44a99daf5925d536c1f19b63127b9c46b59d1 100644
--- a/Source/core/dom/MutationObserverRegistration.cpp
+++ b/Source/core/dom/MutationObserverRegistration.cpp
@@ -146,6 +146,7 @@ void MutationObserverRegistration::trace(Visitor* visitor)
     visitor->trace(m_observer);
     visitor->trace(m_registrationNode);
     visitor->trace(m_registrationNodeKeepAlive);
+    visitor->trace(m_transientRegistrationNodes);
 }
 
 } // namespace WebCore