WebGL 2: validate read buffer attachment when reading from FBO

Source/modules/webgl/WebGLFramebuffer.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 85 matching lines @@
 
     void setHasEverBeenBound() { m_hasEverBeenBound = true; }
 
     bool hasStencilBuffer() const;
 
     // Wrapper for drawBuffersEXT/drawBuffersARB to work around a driver bug.
     void drawBuffers(const Vector<GLenum>& bufs);
 
     GLenum getDrawBuffer(GLenum);
 
+    void readBuffer(const GLenum colorBuffer) { m_readBuffer = colorBuffer; }
+
+    GLenum getReadBuffer() const { return m_readBuffer; }
+
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     explicit WebGLFramebuffer(WebGLRenderingContextBase*);
 
     bool hasObject() const override { return m_object != 0; }
     void deleteObjectImpl(WebGraphicsContext3D*) override;
 
 private:
     WebGLAttachment* getAttachment(GLenum attachment) const;
@@ skipping 11 matching lines @@
     Platform3DObject m_object;
 
     typedef WillBeHeapHashMap<GLenum, RefPtrWillBeMember<WebGLAttachment>> AttachmentMap;
 
     AttachmentMap m_attachments;
 
     bool m_hasEverBeenBound;
 
     Vector<GLenum> m_drawBuffers;
     Vector<GLenum> m_filteredDrawBuffers;
+
+    GLenum m_readBuffer;
 };
 
 } // namespace blink
 
 #endif // WebGLFramebuffer_h