[Sync] Clear LocalDeviceInfoProvider cache on sync DB destruction.

components/sync_driver/local_device_info_provider_impl.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_IMPL_H_
 #define COMPONENTS_SYNC_DRIVER_LOCAL_DEVICE_INFO_PROVIDER_IMPL_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/non_thread_safe.h"
 #include "components/sync_driver/device_info.h"
 #include "components/sync_driver/local_device_info_provider.h"
 #include "components/version_info/version_info.h"
 
 namespace browser_sync {
 
 class LocalDeviceInfoProviderImpl
-    : public sync_driver::LocalDeviceInfoProvider {
+    : public sync_driver::LocalDeviceInfoProvider,
+      public base::NonThreadSafe {
  public:
   LocalDeviceInfoProviderImpl(version_info::Channel channel,
                               const std::string& version,
                               bool is_tablet);
   ~LocalDeviceInfoProviderImpl() override;
 
   // LocalDeviceInfoProvider implementation.
   const sync_driver::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;
 
  private:
   void InitializeContinuation(const std::string& guid,
                               const std::string& signin_scoped_device_id,
                               const std::string& session_name);
 
   // The channel (CANARY, DEV, BETA, etc.) of the current client.
   const version_info::Channel channel_;
 
   // The version string for the current client.
   const std::string version_;
 
   // Whether this device has a tablet form factor (only used on Android
   // devices).
   const bool is_tablet_;
 
   std::string cache_guid_;
   std::unique_ptr<sync_driver::DeviceInfo> local_device_info_;
   base::CallbackList<void(void)> callback_list_;
   base::WeakPtrFactory<LocalDeviceInfoProviderImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(LocalDeviceInfoProviderImpl);
 };
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_SYNC_DRIVER_LOCAL_DEVICE_INFO_PROVIDER_IMPL_H_