[Sync] Emit consents as a separate datatype behind a feature.

If kSyncUserConsentSeparateType feature is enabled (as well as emitting
consents in general), then emit user consents through a separate
datatype instead of user events.

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: I2a8c4423ba71cb8d31740fb9395f431149414610
Reviewed-on: https://chromium-review.googlesource.com/1084835
Reviewed-by: Markus Heintz <[email protected]>
Reviewed-by: Gayane Petrosyan <[email protected]>
Commit-Queue: vitaliii <[email protected]>
Cr-Commit-Position: refs/heads/master@{#565942}
9 files changed