Backward is independent from backends. Test it only with native backend
Backward is independent from backends. Test it only with native backend

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