Replace TabModelObserver's didChangeActiveTab with WebStateListObserver

Replace displayTab/tabSelected from browser_view_controller.mm with
displayWebState/webStateSelected

Bug: 911350
Change-Id: Ief749c48c107672a5c93fc4e51901216d6ee5fa6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585466
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Mohammad Refaat <mrefaat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660382}
5 files changed