When Compositor finishes compositing, it destroys EffectsHandlerImpl,
which in its turn tries to unload all effects. But there is a problem...
EffectsHandlerImpl has platform-specific hooks to ungrab keyboard and
also stop mouse interception. Given that any call made to a virtual function
in the destructor of a base class(EffectsHandlerImpl) won't go to a derived
class(EffectsHandlerImplX11), keyboard won't be ungrabbed even if effect
that grabbed it is already gone.