[Sync] Clear LocalDeviceInfoProvider cache on sync DB destruction.

components/sync_driver/local_device_info_provider_mock.h

 // Copyright 2014 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_LOCAL_DEVICE_INFO_PROVIDER_MOCK_H_
 #define COMPONENTS_SYNC_DRIVER_LOCAL_DEVICE_INFO_PROVIDER_MOCK_H_
 
 #include <string>
 
 #include "components/sync_driver/device_info.h"
@@ skipping 18 matching lines @@
 
   const DeviceInfo* GetLocalDeviceInfo() const override;
   std::string GetSyncUserAgent() const override;
   std::string GetLocalSyncCacheGUID() const override;
   void Initialize(
       const std::string& cache_guid,
       const std::string& signin_scoped_device_id,
       const scoped_refptr<base::TaskRunner>& blocking_task_runner) override;
   std::unique_ptr<Subscription> RegisterOnInitializedCallback(
       const base::Closure& callback) override;
+  void Clear() override;
 
   void Initialize(std::unique_ptr<DeviceInfo> local_device_info);
   void SetInitialized(bool is_initialized);
 
  private:
   bool is_initialized_;
 
   std::unique_ptr<DeviceInfo> local_device_info_;
   base::CallbackList<void(void)> callback_list_;
 };
 
 }  // namespace sync_driver
 
 #endif  // COMPONENTS_SYNC_DRIVER_LOCAL_DEVICE_INFO_PROVIDER_MOCK_H_