Create new signin directory for files related to sync and signin

Sync and Signin files in preferences directory currently does not have an
owner. We want to move these files to a dedicated folder for sync so
that reviewers have a better context about cls.

Bug: 928406
Change-Id: I8137dfbf3f2861ad8507bd1f6843c616e3ab1201
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1657900
Reviewed-by: Theresa <twellington@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Commit-Queue: Tanmoy Mollik <triploblastic@google.com>
Cr-Commit-Position: refs/heads/master@{#672039}
22 files changed