Remove more oilpan.

sky/engine/core/css/CSSCanvasValue.h

 /*
  * Copyright (C) 2008 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 45 matching lines @@
     explicit CSSCanvasValue(const String& name)
         : CSSImageGeneratorValue(CanvasClass)
         , m_canvasObserver(adoptPtr(new CanvasObserverProxy(this)))
         , m_name(name)
         , m_element(nullptr)
     {
     }
 
     // NOTE: We put the CanvasObserver in a member instead of inheriting from it
     // to avoid adding a vptr to CSSCanvasValue.
-    class CanvasObserverProxy final : public DummyBase<CanvasObserverProxy>, public CanvasObserver {
-        WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(CanvasObserverProxy);
+    class CanvasObserverProxy final : public CanvasObserver {
     public:
         explicit CanvasObserverProxy(CSSCanvasValue* ownerValue) : m_ownerValue(ownerValue) { }
 
         virtual void canvasChanged(HTMLCanvasElement* canvas, const FloatRect& changedRect) override
         {
             m_ownerValue->canvasChanged(canvas, changedRect);
         }
         virtual void canvasResized(HTMLCanvasElement* canvas) override
         {
             m_ownerValue->canvasResized(canvas);
@@ skipping 24 matching lines @@
     String m_name;
     // The document supplies the element and owns it.
     RawPtr<HTMLCanvasElement> m_element;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSCanvasValue, isCanvasValue());
 
 } // namespace blink
 
 #endif // CSSCanvasValue_h