Improve broadcast_to
Improve broadcast_to

chainer/chainer,kiyukuta/chainer,AlpacaDB/chainer,ronekko/chainer,anaruse/chainer,cupy/cupy,okuta/chainer,keisuke-umezawa/chainer,pfnet/chainer,hvy/chainer,wkentaro/chainer,ktnyt/chainer,wkentaro/chainer,niboshi/chainer,chainer/chainer,rezoo/chainer,benob/chainer,wkentaro/chainer,sinhrks/chainer,jnishi/chainer,sinhrks/chainer,delta2323/chainer,benob/chainer,cupy/cupy,jnishi/chainer,niboshi/chainer,hvy/chainer,niboshi/chainer,ktnyt/chainer,hvy/chainer,ysekky/chainer,chainer/chainer,cupy/cupy,cemoody/chainer,keisuke-umezawa/chainer,jnishi/chainer,keisuke-umezawa/chainer,chainer/chainer,jnishi/chainer,aonotas/chainer,niboshi/chainer,cupy/cupy,AlpacaDB/chainer,kikusu/chainer,kashif/chainer,ktnyt/chainer,ktnyt/chainer,okuta/chainer,tkerola/chainer,okuta/chainer,wkentaro/chainer,keisuke-umezawa/chainer,okuta/chainer,hvy/chainer,kikusu/chainer