WebGL 2: validate read buffer attachment when reading from FBO

Source/core/html/canvas/WebGLRenderingContextBase.h

Index: Source/core/html/canvas/WebGLRenderingContextBase.h
diff --git a/Source/core/html/canvas/WebGLRenderingContextBase.h b/Source/core/html/canvas/WebGLRenderingContextBase.h
index f8e72ae00baa8859f1fd7fac8676a9e73fa36e94..fa95f198acd3e1d7eaa370c8839b7412e3460848 100644
--- a/Source/core/html/canvas/WebGLRenderingContextBase.h
+++ b/Source/core/html/canvas/WebGLRenderingContextBase.h
@@ -569,6 +569,8 @@ protected:
     bool m_drawBuffersWebGLRequirementsChecked;
     bool m_drawBuffersSupported;
 
+    GLenum m_readbufferOfFBO;
+
     GLint m_packAlignment;
     GLint m_unpackAlignment;
     bool m_unpackFlipY;
@@ -862,6 +864,10 @@ protected:
     // the given format.
     bool validateCompressedTexSubDimensions(const char* functionName, GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, WebGLTexture*);
 
+    // Helper function to validate that the image is attached to read buffer
+    // when reading from FBO (readPixels/copyTexImage2D/copyTexSubImage2D).
+    bool validateReadBufferAttachment(const char* functionName, const WebGLFramebuffer* readFramebufferBinding);
+
     // Helper function to validate mode for draw{Arrays/Elements}.
     bool validateDrawMode(const char* functionName, GLenum);