The update virtual function for GdkGLContext is unused and is a leftover from a previous GL approach. Just remove it. https://bugzilla.gnome.org/show_bug.cgi?id=739750
Implement GdkGLContext using EGL and use hardware mir surfaces when a GdkWindow uses gl rendering. Fixes https://bugzilla.gnome.org/show_bug.cgi?id=740346