[gtk+] Don't initialize GL if it has been disabled

[Matthias Clasen <matthiasc src gnome org>]

commit 1dbc6d91f08e28c90bd39ff8a6137b9480c18510
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Dec 19 12:27:31 2014 -0500

    Don't initialize GL if it has been disabled
    
    We've observed hangs of mutter when it initializes GTK+, which
    are caused by initializing GL, which in turn makes xwayland
    call back into mutter. With this change, mutter should just
    disable GL support in GDK, and things will work.

 gdk/x11/gdkglcontext-x11.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gdk/x11/gdkglcontext-x11.c b/gdk/x11/gdkglcontext-x11.c
index d686768..93bb886 100644
--- a/gdk/x11/gdkglcontext-x11.c
+++ b/gdk/x11/gdkglcontext-x11.c
@@ -586,6 +586,9 @@ gdk_x11_screen_init_gl (GdkScreen *screen)
   if (display_x11->have_glx)
     return TRUE;
 
+  if (_gdk_gl_flags & GDK_GL_DISABLE)
+    return FALSE;
+
   dpy = gdk_x11_display_get_xdisplay (display);
 
   if (!glXQueryExtension (dpy, &error_base, &event_base))