The documentation in https://github.com/flutter/flutter/blob/master/engine/src/flutter/shell/platform/linux/public/flutter_linux/fl_texture_gl.h states:

 * If you want to render textures in other OpenGL context, create and use the
 * #GdkGLContext by calling gdk_window_create_gl_context () with the #GdkWindow
 * of #FlView. The context will be shared with the one used by Flutter.

Since this PR, that's no longer true. The Flutter Linux shell no longer calls gdk_window_create_gl_context therefore you cannot create a shared context with gdk_window_create_gl_context.

I'm only creating this issue because the PR process requires it.