Jank markers are not showing up in the activity tab view when it's using merged threads

[julienw]

See this profile: https://share.firefox.dev/3uuQzOW

There are jank markers as we can see when clicking on the full view button, but we don't see them in the activity tab view (neither in the timeline or the marker chart).

[julienw]

It may be happening because it's a merged thread, and responsiveness data is not properly taken into account in this case. We could copy the responsiveness information from the "main" thread part of this merged thread.

[canova]

We are removing the old active tab view and creating a new one. It's not relevant with the new one anymore, so closing it.