The GSource is created using cogl_glib_source_new which takes a
pointer to a CoglContext. The source calls cogl_poll_get_info() in its
prepare function and cogl_poll_dispatch() in its dispatch
function. The poll FDs on the source are updated according to what
Cogl reports.
The header is only included and the source only compiled if Cogl is
configured with GLib support.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
