BypassWindowManagerHint is a flag which is X11 specific. Because of
that for example QtWayland doesn't create a real window for QWindows
with this flag.
Using such a window will eventually result in a freeze of the whole
application. If one renders with QtQuick to such a window, mesa will
request a frame callback from the compositor. Just the compositor
will never deliver the frame rendered callback as it doesn't know the
window exists in the first place and by that doesn't render it and
will never ever deliver the frame rendered callback.
If now one tries to render another frame, mesa notices that it hasn't
got the frame callback and will block the thread till that happens.
With the setup described: that's until eternity.
See Qt Bug: https://bugreports.qt.io/browse/QTBUG-49272
REVIEW: 125961
ae4ba8920e