[Sync] Update SyncBackendHost to forward ClearServerData to SyncManager

chrome/browser/sync/glue/sync_backend_host_mock.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 CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_MOCK_H_
 #define CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_MOCK_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 90 matching lines @@
 
   void GetAllNodesForTypes(
       syncer::ModelTypeSet types,
       base::Callback<void(const std::vector<syncer::ModelType>& type,
                           ScopedVector<base::ListValue>)> callback) override;
 
   base::MessageLoop* GetSyncLoopForTesting() override;
 
   void RefreshTypesForTest(syncer::ModelTypeSet types) override;
 
+  void ClearServerData(
+      const syncer::SyncManager::ClearServerDataCallback& callback) override;
+
   void set_fail_initial_download(bool should_fail);
 
  private:
   bool fail_initial_download_;
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_MOCK_H_