- Allow hiding individual timeline-tracks to clear up screen space.
- Auto-hide timeline-tracks when there are no entries

Bug: v8:10644
Change-Id: Ibde37242fa1fcb827ca176ee7576a23715c45bda
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2584954Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71739}