GitLab

Add a test that checks if the BrowserTouchBar's
BookmarkTapHelperObserver gets removed when it's destroyed.

Follow up to:
https://chromium-review.googlesource.com/c/chromium/src/+/1099483

Bug: 852222
Change-Id: I60c08a195a8b8adb1848d120c3492783fa615ba9
Reviewed-on: https://chromium-review.googlesource.com/1101484
Commit-Queue: Sarah Chan <spqchan@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568206}