Subsequent invocations reset the trace. This removes the `tracing._reset` method.
Also fixed a bug where BASE element was not reset properly.
Also fixed a bug where tracing would affect the result of protocol call
by setting `callMetadata.error` property.
`tracing._export({ path })` exports current tracing state into a file
and does not require tracing to be stopped.
`tracing._reset()` resets current tracing state, but keeps resources
around so they can be referenced in the future snapshots. Does not stop.
The usage pattern is:
```js
await tracing.start({ screenshots: true, snapshots: true });
// ...
await tracing._reset();
// Do stuff, it will all be in the export below.
await tracing._export({ path });
// ...
await tracing.stop();
```
There are a few ways for `connect()` to finish:
- `Browser.close()` from the client side.
- Browser on the server side did exit (e.g. crashed).
- Connection was dropped by either of the sides.
We reduce all the cases to the last one by dropping the
connection when client wants calls `Browser.close()` or
server-side browser exits.
In all these cases we should properly cleanup on the server side,
and ensure that all promises reject on the client side.
