implement getBufferSubDataAsync prototype

third_party/WebKit/Source/modules/webgl/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 631 matching lines @@
   bool isAccelerated() const override { return true; }
   void setIsHidden(bool) override;
   bool paintRenderingResultsToCanvas(SourceDrawingBuffer) override;
   WebLayer* platformLayer() const override;
   void stop() override;
 
   void addSharedObject(WebGLSharedObject*);
   void addContextObject(WebGLContextObject*);
   void detachAndRemoveAllObjects();
 
-  void destroyContext();
+  virtual void destroyContext();
   void markContextChanged(ContentChangeType);
 
   void onErrorMessage(const char*, int32_t id);
 
   void notifyCanvasContextChanged();
 
   // Query if depth_stencil buffer is supported.
   bool isDepthStencilSupported() { return m_isDepthStencilSupported; }
 
   // Helper to return the size in bytes of OpenGL data types
@@ skipping 887 matching lines @@
                   context,
                   context->is3d(),
                   context.is3d());
 
 }  // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(
     blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif  // WebGLRenderingContextBase_h