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The new State encompasses (and should eventually largely replace) the
following state getters:
- CanSyncStart
- IsEngineInitialized
- GetAuthError
- IsFirstSetupComplete
- HasUnrecoverableError
- IsSyncActive
- ConfigurationDone

Other SyncService state that it *not* packed into the enum:
- Setup in progress
- Encryption
- Anything that's per-ModelType
- Local Sync

Bug: 839834
Change-Id: Iec1c3d744ffcb33fceccfe0bb0d028cc17203655
Reviewed-on: https://chromium-review.googlesource.com/1102331
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571110}