Oilpan: disable conservative GCs during initial GC mixin construction.

Source/core/html/shadow/MediaControlElementTypes.h

 /*
  * Copyright (C) 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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.
@@ skipping 96 matching lines @@
 protected:
     MediaControlDivElement(MediaControls&, MediaControlElementType);
 
 private:
     virtual bool isMediaControlElement() const override final { return true; }
 };
 
 // ----------------------------
 
 class MediaControlInputElement : public HTMLInputElement, public MediaControlElement {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(MediaControlInputElement);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN_NESTED(MediaControlInputElement, HTMLFormControlElement);
 public:
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     MediaControlInputElement(MediaControls&, MediaControlElementType);
 
 private:
     virtual void updateDisplayType() { }
     virtual bool isMediaControlElement() const override final { return true; }
     virtual bool isMouseFocusable() const override;
 };
 
 // ----------------------------
 
 class MediaControlTimeDisplayElement : public MediaControlDivElement {
 public:
     void setCurrentValue(double);
     double currentValue() const { return m_currentValue; }
 
 protected:
     MediaControlTimeDisplayElement(MediaControls&, MediaControlElementType);
 
 private:
     double m_currentValue;
 };
 
 } // namespace blink
 
 #endif // MediaControlElementTypes_h