Prefer syncer::SyncService over browser_sync::ProfileSyncService

SyncService is the interface, ProfileSyncService is the concrete
implementation. Generally no clients should need to use the conrete
implementation - for one, testing will be much easier once everyone
uses the interface only.

This CL trivially replaces most remaining usages of ProfileSyncService
with SyncService.

Bug: 924508
Change-Id: Ibcd2f648468be39250df9f43e17af7f7b11fdf4d
Reviewed-on: https://chromium-review.googlesource.com/c/1454554
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Fabio Tirelo <ftirelo@chromium.org>
Reviewed-by: Nathan Parker <nparker@chromium.org>
Reviewed-by: calamity <calamity@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631203}
15 files changed