Clutter discards any motion event if next event happens to also be a
motion event. This is problematic when the motion event carries
relative motion deltas, since the information about them is completely
lost.

Until we have moved away made the stage stop discarding motion events,
lets work around the issue by compressing them, effectively adding
multiple relative motion deltas together, would one be discarded.

https://bugzilla.gnome.org/show_bug.cgi?id=771049