Bug fixes:

* Wrong time range selection of timeline chunks handled by mouse events.
* Consecutive file uploads does not create a new Model object causing
bugs on timeline-track start and end times.

Bug: v8:10644

Change-Id: I3d31ddda1ffca70c18c87dd103f2b788713c2911
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2379863Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Zeynep Cankara <zcankara@google.com>
Cr-Commit-Position: refs/heads/master@{#69598}