Avoid duplicate hash lookups in CustomElementScheduler::ensureCallbackQueue

Source/core/dom/custom/CustomElementScheduler.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 45 matching lines @@
     static CustomElementMicrotaskImportStep* scheduleImport(HTMLImportChild*);
 
     static void microtaskDispatcherDidFinish();
     static void callbackDispatcherDidFinish();
 
 private:
     CustomElementScheduler() { }
 
     static CustomElementScheduler& instance();
 
-    CustomElementCallbackQueue* ensureCallbackQueue(PassRefPtr<Element>);
-    CustomElementCallbackQueue* schedule(PassRefPtr<Element>);
+    CustomElementCallbackQueue& ensureCallbackQueue(PassRefPtr<Element>);
+    CustomElementCallbackQueue& schedule(PassRefPtr<Element>);
 
     // FIXME: Consider moving the element's callback queue to
     // ElementRareData. Then the scheduler can become completely
     // static.
     void clearElementCallbackQueueMap();
 
     // The element -> callback queue map is populated by the scheduler
     // and owns the lifetimes of the CustomElementCallbackQueues.
     typedef HashMap<Element*, OwnPtr<CustomElementCallbackQueue> > ElementCallbackQueueMap;
     ElementCallbackQueueMap m_elementCallbackQueueMap;
 };
 
 }
 
 #endif // CustomElementScheduler_h