Migrate extensions tests to SyncUserSettings

SyncUserSettings is a new class that encapsulates all the
user-configurable knobs for Sync. It replaces a bunch of setters
and getters directly on the SyncService.

Bug: 884159
Change-Id: Ic69d65e6f4a2f6e74f8ca0fd3954aaf78b0992fa
Reviewed-on: https://chromium-review.googlesource.com/c/1338100
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609623}
2 files changed