format: Chrome Trace with instant samples

👋🏻 Hi!

I was trying to visualise the following Chrome Trace in speedscope, but unfortunately, I get an error.

```json
{
"traceEvents": [
{"name": "hi", "cat": "none", "ph": "i", "pid": 22630, "tid": 22630, "ts": 829, "stack": ["a", "b", "c"]},
],
"displayTimeUnit": "ns",
"otherData": {
"version": "none"
},
"samples": []
}
```

I have it stored under `test.json`, and either dragging it or selecting it in the file browser results in this alert:

> Unrecognized format! See documentation about supported formats.

Perhaps I have misunderstood something about the Chrome Trace format, or I have made some mistake. I have tried on [Perfetto](https://ui.perfetto.dev/) and it worked (almost) right. Notice the missing stacks. But perhaps I don't know how to use its UI 😅 .