[Sync] Update SyncBackendHost to forward ClearServerData to SyncManager

sync/internal_api/sync_backup_manager.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 SYNC_INTERNAL_API_SYNC_BACKUP_MANAGER_H_
 #define SYNC_INTERNAL_API_SYNC_BACKUP_MANAGER_H_
 
 #include <set>
 
 #include "sync/internal_api/sync_rollback_manager_base.h"
@@ skipping 20 matching lines @@
       const syncable::ImmutableWriteTransactionInfo& write_transaction_info,
       syncable::BaseTransaction* trans) override;
 
   void RegisterDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer) override;
   void UnregisterDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer) override;
   bool HasDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer) override;
   void RequestEmitDebugInfo() override;
+  void ClearServerData(const ClearServerDataCallback& callback) override;
 
  private:
   // Replaces local IDs with server IDs and clear unsynced bit of modified
   // entries.
   void NormalizeEntries();
 
   // Manipulate preference nodes so that they'll be overwritten by local
   // preference values during model association, i.e. local wins instead of
   // server wins. This is for preventing backup from changing preferences in
   // case backup DB has hijacked preferences.
   void HideSyncPreference(ModelType pref_type);
 
   // Handles of unsynced entries caused by local model changes.
   std::set<int64> unsynced_;
 
   // True if NormalizeEntries() is being called.
   bool in_normalization_;
 
   SyncStatus status_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackupManager);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_SYNC_BACKUP_MANAGER_H_