[profiler] fix chrome tracing for profiler run with cuda (#33987)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33987
There was an error in
https://github.com/pytorch/pytorch/pull/30724/files that resulted in
`export_chrome_trace` generating invalid JSON. This only came up when the
profiler is run with `use_cuda=True` from what it looks like. In the future, we
should have tests that ensure we generate valid JSON because we no longer use
the json library.
Test Plan: Add UT to validate JSON.
Differential Revision: D20171428
fbshipit-source-id: ec135a154ce33f62b78d98468174dce4cf01fedf
