[Sync] Move sync thread ownership to ProfileSyncService.

components/browser_sync/profile_sync_service.h

Index: components/browser_sync/profile_sync_service.h
diff --git a/components/browser_sync/profile_sync_service.h b/components/browser_sync/profile_sync_service.h
index aea88e76a7f8975be38b2266e731022c813cf79d..2d88797fc5a5f70a7efb8c8417b1014bccf843ec 100644
--- a/components/browser_sync/profile_sync_service.h
+++ b/components/browser_sync/profile_sync_service.h
@@ -921,11 +921,7 @@ class ProfileSyncService : public syncer::SyncService,
   // and association information.
   syncer::WeakHandle<syncer::DataTypeDebugInfoListener> debug_info_listener_;
 
-  // A thread where all the sync operations happen.
-  // OWNERSHIP Notes:
-  //     * Created when backend starts for the first time.
-  //     * If sync is disabled, PSS claims ownership from backend.
-  //     * If sync is reenabled, PSS passes ownership to new backend.
+  // The thread where all the sync operations happen.
   std::unique_ptr<base::Thread> sync_thread_;

[Nicolas Zea, 2016/11/07 20:29:46]

I think it's worth explaining the lifetime of this thread here (including the
various subtle issues we discussed, for example mentioning that although we do
join on shutdown, http requests have their own cancelation logic).

[maxbogue, 2016/11/07 23:12:05]

Done, PTAL!

 
   // ProfileSyncService uses this service to get access tokens.