Comment 2 for bug 1017402

StacktraceTop:
 ?? ()
 unity::ui::EdgeBarrierController::Impl::OnPointerBarrierEvent (this=0x2e61170, owner=0x3482220, event=...) at /build/buildd/unity-5.12/plugins/unityshell/src/EdgeBarrierController.cpp:139
 operator() (_A_a2=..., _A_a1=<optimized out>, this=<optimized out>) at /usr/include/sigc++-2.0/sigc++/functors/mem_fun.h:1917
 operator()<unity::ui::PointerBarrierWrapper* const&, const std::shared_ptr<unity::ui::BarrierEvent>&> (_A_arg2=..., _A_arg1=<optimized out>, this=<optimized out>) at /usr/include/sigc++-2.0/sigc++/adaptors/adaptor_trait.h:103
 sigc::internal::slot_call2<sigc::bound_mem_functor2<void, unity::ui::EdgeBarrierController::Impl, unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent> >, void, unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent> >::call_it (rep=<optimized out>, a_1=<optimized out>, a_2=...) at /usr/include/sigc++-2.0/sigc++/functors/slot.h:173