[Sync] Wire ConsentSyncBridge behind a feature on iOS.

Connect ConsentSyncBridge to ConsentAuditor behind a feature
on iOS. ConsentAuditor does not use the bridge at all yet.

The bridge is wired to the auditor on all other platforms in

This CL is a part of a series to split user consents from user events
into a separate datatype.

Bug: 840357
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ie47fb3241cfdd64f7962d9d8b62f28578a76c0a1
Reviewed-on: https://chromium-review.googlesource.com/1087269
Reviewed-by: Markus Heintz <markusheintz@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: vitaliii <vitaliii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569995}
3 files changed