[Tab Group Parity] Do not save title on dismiss if text left empty

In the group creation dialog, if the title field is left empty and the
user dismisses the dialog, do not save the empty string text field and
leave the title as null so it is dynamically adapted to the group size.

Bug: 41490324
Change-Id: Icaf258617e6cd79e22a9c16bb9c4dd9c4f1dd88d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5440139
Reviewed-by: Sky Malice <skym@chromium.org>
Commit-Queue: Brandon Fong <bjfong@google.com>
Cr-Commit-Position: refs/heads/main@{#1285469}