Bug 1299956 - Better use of kungFuDeathGrip in EventListenerManager, r=smaug

dom/events/EventListenerManager.cpp

@@ -655,6 +655,8 @@ EventListenerManager::RemoveEventListenerInternal(
   uint32_t typeCount = 0;
   bool deviceType = IsDeviceType(aEventMessage);
 
+  RefPtr<EventListenerManager> kungFuDeathGrip(this);
+
   for (uint32_t i = 0; i < count; ++i) {
     listener = &mListeners.ElementAt(i);
     if (EVENT_TYPE_EQUALS(listener, aEventMessage, aUserType, aTypeString,
@@ -662,7 +664,6 @@ EventListenerManager::RemoveEventListenerInternal(
       ++typeCount;
       if (listener->mListener == aListenerHolder &&
           listener->mFlags.EqualsForRemoval(aFlags)) {
-        RefPtr<EventListenerManager> kungFuDeathGrip(this);
         mListeners.RemoveElementAt(i);
         --count;
         NotifyEventListenerRemoved(aUserType);