[Sync] Move sync thread ownership to ProfileSyncService.

components/browser_sync/profile_sync_service.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_BROWSER_SYNC_PROFILE_SYNC_SERVICE_H_
 #define COMPONENTS_BROWSER_SYNC_PROFILE_SYNC_SERVICE_H_
 
 #include <memory>
 #include <set>
 #include <string>
@@ skipping 903 matching lines @@
 
   syncer::DataTypeManager::ConfigureStatus configure_status_;
 
   // The set of currently enabled sync experiments.
   syncer::Experiments current_experiments_;
 
   // Sync's internal debug info listener. Used to record datatype configuration
   // 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.
   ProfileOAuth2TokenService* const oauth2_token_service_;
 
   // ProfileSyncService needs to remember access token in order to invalidate it
   // with OAuth2TokenService.
   std::string access_token_;
 
   // ProfileSyncService needs to hold reference to access_token_request_ for
   // the duration of request in order to receive callbacks.
@@ skipping 68 matching lines @@
   base::WeakPtrFactory<ProfileSyncService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileSyncService);
 };
 
 bool ShouldShowActionOnUI(const syncer::SyncProtocolError& error);
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_BROWSER_SYNC_PROFILE_SYNC_SERVICE_H_