WebGL 2: add readPixels API to read pixels into pixel pack buffer

Source/modules/webgl/WebGLBuffer.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 24 matching lines @@
 public:
     ~WebGLBuffer() override;
 
     static WebGLBuffer* create(WebGLRenderingContextBase*);
 
     GLenum getInitialTarget() const { return m_initialTarget; }
     void setInitialTarget(GLenum);
 
     bool hasEverBeenBound() const { return object() && m_initialTarget; }
 
+    void setSize(long long size) { m_size = size; }
+    long long getSize() const { return m_size; }
+
 protected:
     explicit WebGLBuffer(WebGLRenderingContextBase*);
 
     void deleteObjectImpl(WebGraphicsContext3D*) override;
 
 private:
     bool isBuffer() const override { return true; }
 
     GLenum m_initialTarget;
+    long long m_size;
 };
 
 } // namespace blink
 
 #endif // WebGLBuffer_h