Fix test/test_proxy_tensor (#99415)
test_proxy_tensor fails when run by itself (python test/test_proxy_tensor.py -v),
but not when all of the tests are run together.
The cause is that torch._dynamo isn't imported in
torch/fx/experimenta/proxy_tensor.py but it is using functions from the
torch._dynamo package.
The fix in this PR is to add the import statements. In the future we can
consider always importing torch._dynamo on `import torch` or moving the
import to the top of the file, but there are some serious circular
dependencies to be worked out.
NB: an import in the middle of the file makes the function a bit slow
the first time the import happens but all subsequent calls are fast.
Test Plan:
- python test/test_proxy_tensor.py
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99415
Approved by: https://github.com/soulitzer
