Prior to this fix, the variables 'enter_event' and 'leave_event' in the
handler for the 'changed' event for the
'/org/gnome/shell/extensions/dock/hide_effect' dconf key were
uninitialized. This made switching the hide effect at runtime throw an
error. By promoting these two variables to instance members and
assigning to them upon initialization, this problem should be fixed.
https://bugzilla.gnome.org/show_bug.cgi?id=662389
Stefan 'psYchotic' Zwanenburg
b7e30eb99a