Comment 17 for bug 1510941

Another go, now with more assertions:

commit dab1c0f159d74fc82618b88262e064010e6387ec
Author: Chris Wilson <email address hidden>
Date: Tue Aug 18 23:27:22 2015 +0100

    sna/dri2: Move the pending swap from the buffer to the event

    To ease tracking of the next swap, stash it on the event (which is then
    reused) rather than the back buffer (which changes frequently).

    In addition, add debug flags and assertions to track event stages (such
    as making sure we do not decouple/free an event that we have sent a
    signal back to the client).

As always hopefully this gets us to the point of chasing down the original bug!