- Add tests and fix Chunk calculations in Timeline class
- Cache DOM nodes directly as properties in TimelineTrackBase
- Keep track of last focused entry in timeline tracks and reuse it
  to position the tooltip when the view is locked

Bug: v8:10644
Change-Id: I356dcf7eed220df89f6a7ff926f00f78b119160e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2968943
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75224}