GitLab

for the collapsed TabWidthConstraint.

When the tab group collapses, the available tabstrip width is not
updated to reflect the collapsed group.
Also easier and less code >_>

Bug: 1018230
Change-Id: If3e0907ce3b881e736c748a6db7b040e66a5c172
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207617
Commit-Queue: Charlene Yan <cyan@chromium.org>
Reviewed-by: Connie Wan <connily@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769980}