[Sync] Pass a TaskRunner into SBHI/SBHC, not a thread or message loop.

components/sync/driver/glue/sync_backend_host_impl.h

 // Copyright 2013 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_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_IMPL_H_
 #define COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 44 matching lines @@
  public:
   typedef SyncStatus Status;
 
   // Create a SyncBackendHost with a reference to the |frontend| that
   // it serves and communicates to via the SyncFrontend interface (on
   // the same thread it used to call the constructor).  Must outlive
   // |sync_prefs|.
   SyncBackendHostImpl(
       const std::string& name,
       SyncClient* sync_client,
-      const scoped_refptr<base::SingleThreadTaskRunner>& ui_thread,
       invalidation::InvalidationService* invalidator,
       const base::WeakPtr<SyncPrefs>& sync_prefs,
       const base::FilePath& sync_folder);
   ~SyncBackendHostImpl() override;
 
   // SyncBackendHost implementation.
   void Initialize(
       SyncFrontend* frontend,
-      base::Thread* sync_thread,
+      scoped_refptr<base::SingleThreadTaskRunner> sync_task_runner,
       const WeakHandle<JsEventHandler>& event_handler,
       const GURL& service_url,
       const std::string& sync_user_agent,
       const SyncCredentials& credentials,
       bool delete_sync_data_folder,
       bool enable_local_sync_backend,
       const base::FilePath& local_sync_backend_folder,
       std::unique_ptr<SyncManagerFactory> sync_manager_factory,
       const WeakHandle<UnrecoverableErrorHandler>& unrecoverable_error_handler,
       const base::Closure& report_unrecoverable_error_function,
@@ skipping 196 matching lines @@
   void HandleLocalSetPassphraseEncryptionOnFrontendLoop(
       const SyncEncryptionHandler::NigoriState& nigori_state);
 
   // Dispatched to from OnConnectionStatusChange to handle updating
   // frontend UI components.
   void HandleConnectionStatusChangeOnFrontendLoop(ConnectionStatus status);
 
   void ClearServerDataDoneOnFrontendLoop(
       const SyncManager::ClearServerDataCallback& frontend_callback);
 
-  // A reference to the TaskRUnner used to construct |this|, so we know how to
-  // safely talk back to the SyncFrontend.
-  scoped_refptr<base::SingleThreadTaskRunner> const frontend_task_runner_;
-
   SyncClient* const sync_client_;
 
-  // A pointer to the sync thread.
-  base::Thread* sync_thread_;
-
-  // The UI thread's task runner.
-  const scoped_refptr<base::SingleThreadTaskRunner> ui_thread_;
+  // The task runner where all the sync engine operations happen.
+  scoped_refptr<base::SingleThreadTaskRunner> sync_task_runner_;
 
   // Name used for debugging (set from profile_->GetDebugName()).
   const std::string name_;
 
   // Our core, which communicates directly to the syncapi. Use refptr instead
   // of WeakHandle because |core_| is created on UI loop but released on
   // sync loop.
   scoped_refptr<SyncBackendHostCore> core_;
 
   // A handle referencing the main interface for non-blocking sync types. This
@@ skipping 28 matching lines @@
   // If an explicit passphrase is in use, the time at which the passphrase was
   // first set (if available).
   base::Time cached_explicit_passphrase_time_;
 
   // UI-thread cache of the last SyncCycleSnapshot received from syncapi.
   SyncCycleSnapshot last_snapshot_;
 
   invalidation::InvalidationService* invalidator_;
   bool invalidation_handler_registered_;
 
+  // Checks that we're on the same thread this was constructed on (UI thread).
+  base::ThreadChecker thread_checker_;
+
   base::WeakPtrFactory<SyncBackendHostImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHostImpl);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_IMPL_H_