Use graph scope in check_backward_test.cc
Use graph scope in check_backward_test.cc

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