Roman Gilg authored Mar 13, 2018 and Adam Jackson committed Mar 28, 2018

Introduce support for Present's window flip mode. The support is not yet
complete, but works reasonable well for the most important use case, that
is fullscreen applications.

We take a Present flip and if the xwl_window->window has the same dimensions
as the presenting window, the flip is represented by a wl_buffer and attached
to the main wl_surface of the xwl_window.

After commit we are listening for the sync callback in order to tell Present,
that the pixmap flip is not longer pending, for the frame callback in order
to update the msc counter and for the buffer release callback in order to tell
Present that the pixmap is idle again.

The following functionality is missing from this patch:
* (slowed down) flips in case the compositor is not sending frame callbacks,
* queuing events to MSC times,
* per window flips for child windows with smaller size than the xwl_window.

To make use of this functionality Xwayland must run rootless and with
Glamor/GBM.

Signed-off-by: Roman Gilg <subdiff@gmail.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>