Remove more oilpan.

sky/engine/core/html/canvas/WebGLRenderingContextBase.h

Index: sky/engine/core/html/canvas/WebGLRenderingContextBase.h
diff --git a/sky/engine/core/html/canvas/WebGLRenderingContextBase.h b/sky/engine/core/html/canvas/WebGLRenderingContextBase.h
index 00648a5597fa4f4f52488dc5d4fdb93c3b9403b9..6a55fb7ee99b62e87702caa887ffdd4a3283aff8 100644
--- a/sky/engine/core/html/canvas/WebGLRenderingContextBase.h
+++ b/sky/engine/core/html/canvas/WebGLRenderingContextBase.h
@@ -99,7 +99,6 @@ class WebGLRenderingContextLostCallback;
 class WebGLRenderingContextErrorMessageCallback;
 
 class WebGLRenderingContextBase: public CanvasRenderingContext, public ActiveDOMObject, public Page::MultisamplingChangedObserver {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(WebGLRenderingContextBase);
 public:
     virtual ~WebGLRenderingContextBase();
 
@@ -573,7 +572,7 @@ protected:
         DraftExtension                  = 0x01,
     };
 
-    class ExtensionTracker : public DummyBase<ExtensionTracker> {
+    class ExtensionTracker {
     public:
         ExtensionTracker(ExtensionFlags flags, const char* const* prefixes)
             : m_draft(flags & DraftExtension)