[Sync] Allow sync start without sign-in if the local sync backend is on.

components/sync/driver/fake_sync_service.h

 // Copyright 2015 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_FAKE_SYNC_SERVICE_H_
 #define COMPONENTS_SYNC_DRIVER_FAKE_SYNC_SERVICE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 10 matching lines @@
 class FakeSyncService : public SyncService {
  public:
   FakeSyncService();
   ~FakeSyncService() override;
 
  private:
   // SyncService:
   bool IsFirstSetupComplete() const override;
   bool IsSyncAllowed() const override;
   bool IsSyncActive() const override;
+  bool IsLocalSyncEnabled() const override;
   void TriggerRefresh(const ModelTypeSet& types) override;
   ModelTypeSet GetActiveDataTypes() const override;
   SyncClient* GetSyncClient() const override;
   void AddObserver(SyncServiceObserver* observer) override;
   void RemoveObserver(SyncServiceObserver* observer) override;
   bool HasObserver(const SyncServiceObserver* observer) const override;
   void OnDataTypeRequestsSyncStartup(ModelType type) override;
   bool CanSyncStart() const override;
   void RequestStop(SyncService::SyncStopDataFate data_fate) override;
   void RequestStart() override;
@@ skipping 48 matching lines @@
 
   GoogleServiceAuthError error_;
   GURL sync_service_url_;
   std::string unrecoverable_error_message_;
   std::unique_ptr<UserShare> user_share_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_FAKE_SYNC_SERVICE_H_