Enhancement idea: allow making parent tracks "sticky" when scrolling

It would be nice for me to always see the parent tracks of the first visible track when I scroll, similar to vscode sticky scroll.

It seems from the docs that there's already such a feature when tracks are created by plugins. From https://perfetto.dev/docs/contributing/ui-plugins:

> isSummary: boolean (default false): If true, this track acts as a summary for its children. It gets special styling and behavior (e.g., sticky when expanded).

I wouldn't mind for this to be always on, but I guess there are good reasons not to do that. In that case, one or both of those would be great:
* A setting to enable this behavior
* A field in the protobuf format that would allow me to enable this in the files I generate.

Thanks!
Noam

Start with the UI plugin documentation linked in the issue and inspect the existing summary-track behavior described there. Trace how parent and child tracks are represented in the UI and how generated protobuf data defines tracks. Done means agreeing on and implementing either a UI setting or a protobuf-supported way to make parent tracks sticky, with corresponding coverage.

Written by the indexing model from the issue text.