Add initial prototype.

3-mid/opengl/source/platform/egl/private/opengl-surface-privvy.adb

@@ -0,0 +1,10 @@
+package body opengl.Surface.privvy
+is
+
+   function to_eGL (Self : in Surface.item'Class) return egl.EGLSurface
+   is
+   begin
+      return Self.egl_Surface;
+   end to_eGL;
+
+end opengl.Surface.privvy;