GitLab

This CL includes:
- Add build rule +components/prefs to os_crypt component.
- Add a preference key creation.
- Implement utility tool to get/set the preference.

Bug: 791541
Change-Id: I50835a6edeb62aaef28566d08162accf7789c8eb
Reviewed-on: https://chromium-review.googlesource.com/1183361Reviewed-by: Dominic Battré <battre@chromium.org>
Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Tonko Sabolčec <tsabolcec@google.com>
Cr-Commit-Position: refs/heads/master@{#585760}