Use integer floor division for pooling shape computation (#22304)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/21935 by using the integer floor division that was introduced for convolution shapes in https://github.com/pytorch/pytorch/issues/9640. Without this fix, the pooling operators can produce a 1-element output in cases they shouldn't.
Disclaimer: I couldn't properly test it locally (it's not picking up the modified version for some reason). I'm marking this WIP until I checked what the CI tools say...
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22304
Differential Revision: D16181955
Pulled By: ezyang
fbshipit-source-id: a2405372753572548b40616d1206848b527c8121
