Oilpan: disable conservative GCs during initial GC mixin construction.

Source/core/html/canvas/WebGLRenderingContextBase.h

 /*
  * Copyright (C) 2009 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 86 matching lines @@
 class WebGLSharedObject;
 class WebGLSharedWebGraphicsContext3D;
 class WebGLTexture;
 class WebGLUniformLocation;
 class WebGLVertexArrayObjectOES;
 
 class WebGLRenderingContextLostCallback;
 class WebGLRenderingContextErrorMessageCallback;
 
 class WebGLRenderingContextBase : public CanvasRenderingContext, public Page::MultisamplingChangedObserver, public ScriptWrappable {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(WebGLRenderingContextBase);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN_NESTED(WebGLRenderingContextBase, CanvasRenderingContext);
 public:
     virtual ~WebGLRenderingContextBase();
 
     virtual unsigned version() const = 0;
     virtual String contextName() const = 0;
     virtual void registerContextExtensions() = 0;
 
     static unsigned getWebGLVersion(const CanvasRenderingContext*);
 
     static PassOwnPtr<blink::WebGraphicsContext3D> createWebGraphicsContext3D(HTMLCanvasElement*, WebGLContextAttributes, unsigned webGLVersion);
@@ skipping 869 matching lines @@
     static IntSize oldestContextSize();
 };
 
 DEFINE_TYPE_CASTS(WebGLRenderingContextBase, CanvasRenderingContext, context, context->is3d(), context.is3d());
 
 } // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif // WebGLRenderingContextBase_h