COGL bug http://bugzilla.openedhand.com/show_bug.cgi?id=2110 results
in pending drawing at the time of cogl_offscreen_new_to_texture() going
to the newly created framebuffer rather than the stage.
This would result in most windows being missing for the first frame
when a new window is mapped.
Work around this by calling cogl_flush() before
cogl_offscreen_new_to_texture().
https://bugzilla.gnome.org/show_bug.cgi?id=618138
092cc47afc
