Prefer using SyncService (the interface) over ProfileSyncService (the impl)

It's better to use the interface rather than the concrete implementation.
For one, this will make testing easier.

This CL trivially switches a bunch of uses of ProfileSyncService over to
SyncService. There are still many left.

Bug: 910518
Change-Id: I6890db739b3333c056c6b6631d2074a8fd3f2efe
Reviewed-on: https://chromium-review.googlesource.com/c/1375718
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616325}
17 files changed