GitLab

Break up tabs related functionality to MultiTabStory to be more
reusable in other features.

Bug: 1099917
Change-Id: I7e1310ee4c680383b5347e1f046b7bb718e35837
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631465
Commit-Queue: Yuheng Huang <yuhengh@chromium.org>
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844341}