SyncAuthManager: Properly handle exiting the Sync-paused state

Before this CL, this was broken if kStopSyncInPausedState was enabled:
Entering "Sync paused" would shut down the Sync machinery, but exiting
that state didn't start it up again. This CL fixes that by making
SyncAuthManager notify the SyncService when exiting "Sync paused", so
that the SyncService can then decide if it should start up again.

This CL also updates SyncAuthTest.SyncPausedState so that is passes
both with and without kStopSyncInPausedState.

Bug: 954195
Change-Id: I9412408b1c3b868a71574d1f70a49782636d8de3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1581959
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653572}
3 files changed