GitLab

- Added a skeleton of SharingService with 3 APIs, implementation is
  empty for now
- Added a proto for SharingMessage
- Added definition of handler for SharingMessage
- SharingService is initialized with a profile
- Added OWNERS file

Bug: 966028
Change-Id: I8beb1d001b8186b7259c7421f6d6d906bcf4a2f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627367
Commit-Queue: Alex Chau <alexchau@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Auto-Submit: Alex Chau <alexchau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664238}