[Sync] Move thread checking into the ModelSafeWorker interface.

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 227 matching lines @@
     std::unique_ptr<syncer::SyncClient> sync_client;
     std::unique_ptr<SigninManagerWrapper> signin_wrapper;
     ProfileOAuth2TokenService* oauth2_token_service = nullptr;
     GaiaCookieManagerService* gaia_cookie_manager_service = nullptr;
     StartBehavior start_behavior = MANUAL_START;
     syncer::NetworkTimeUpdateCallback network_time_update_callback;
     base::FilePath base_directory;
     scoped_refptr<net::URLRequestContextGetter> url_request_context;
     std::string debug_identifier;
     version_info::Channel channel = version_info::Channel::UNKNOWN;
-    scoped_refptr<base::SingleThreadTaskRunner> db_thread;
-    scoped_refptr<base::SingleThreadTaskRunner> file_thread;
     base::SequencedWorkerPool* blocking_pool = nullptr;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(InitParams);
   };
 
   explicit ProfileSyncService(InitParams init_params);
 
   ~ProfileSyncService() override;
 
@@ skipping 559 matching lines @@
   // The request context in which sync should operate.
   scoped_refptr<net::URLRequestContextGetter> url_request_context_;
 
   // An identifier representing this instance for debugging purposes.
   std::string debug_identifier_;
 
   // The product channel of the embedder.
   version_info::Channel channel_;
 
   // Threading context.
-  scoped_refptr<base::SingleThreadTaskRunner> db_thread_;
-  scoped_refptr<base::SingleThreadTaskRunner> file_thread_;
   base::SequencedWorkerPool* blocking_pool_;
 
   // Indicates if this is the first time sync is being configured.  This value
   // is equal to !IsFirstSetupComplete() at the time of OnBackendInitialized().
   bool is_first_time_sync_configure_;
 
   // Number of UIs currently configuring the Sync service. When this number
   // is decremented back to zero, Sync setup is marked no longer in progress.
   int outstanding_setup_in_progress_handles_ = 0;
 
@@ skipping 166 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_