Fix CHROMIUM_EVENT_LOG being none
Summary:
X-link: https://github.com/pytorch/pytorch/pull/154258
It turns out if you import something that's None at import time in python, and later update the value, the one you imported stays none:
```
import torch
from torch._dynamo.utils import CHROMIUM_EVENT_LOG
class Foo:
pass
torch._dynamo.utils.CHROMIUM_EVENT_LOG = Foo()
print(CHROMIUM_EVENT_LOG) # None
```
This fixes teh bug so we get AOTAutogradCache instant events again
ghstack-source-id: 285913063
exported-using-ghexport
Reviewed By: Myrthan, oulgen
Differential Revision: D75305770
fbshipit-source-id: b2e1692b80216ae59e7409472565a903ffbc64d2
