Previously the frame callback list was tracked as part of the global
compositor state. This patch moves the list to be part of the surface
state like it is in Weston. The frame callback now iterates the list
of surfaces to flush all of the callbacks. This change will be useful
when the example is converted to use subsurfaces so that it can have a
separate frame callback for the subsurface and flush the list for an
individual client surface rather than flushing globally.
f9b2541df1