Remove more oilpan.

sky/engine/core/dom/custom/CustomElementObserver.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 20 matching lines @@
 #ifndef CustomElementObserver_h
 #define CustomElementObserver_h
 
 #include "platform/heap/Handle.h"
 #include "wtf/HashMap.h"
 
 namespace blink {
 
 class Element;
 
-class CustomElementObserver : public DummyBase<CustomElementObserver> {
+class CustomElementObserver {
 public:
     virtual ~CustomElementObserver() { }
 
     // API for CustomElement to kick off notifications
 
     static void notifyElementDidFinishParsingChildren(Element*);
     static void notifyElementWasDestroyed(Element*);
 
     virtual void trace(Visitor*) { }
 
 protected:
     CustomElementObserver() { }
 
     void observe(Element*);
     void unobserve(Element*);
 
     virtual void elementDidFinishParsingChildren(Element*) = 0;
     virtual void elementWasDestroyed(Element* element) { unobserve(element); }
 };
 
 }
 
 #endif // CustomElementObserver_h