Support Variable.to_cpu, to_gpu from ChainerX
Support Variable.to_cpu, to_gpu from ChainerX

keisuke-umezawa/chainer,jnishi/chainer,jnishi/chainer,ktnyt/chainer,niboshi/chainer,hvy/chainer,keisuke-umezawa/chainer,ktnyt/chainer,wkentaro/chainer,niboshi/chainer,okuta/chainer,chainer/chainer,hvy/chainer,jnishi/chainer,chainer/chainer,jnishi/chainer,hvy/chainer,okuta/chainer,chainer/chainer,niboshi/chainer,okuta/chainer,keisuke-umezawa/chainer,niboshi/chainer,ktnyt/chainer,okuta/chainer,pfnet/chainer,keisuke-umezawa/chainer,wkentaro/chainer,chainer/chainer,wkentaro/chainer,ktnyt/chainer,tkerola/chainer,hvy/chainer,wkentaro/chainer