[Sync] Replace ClearServerDataCallback with Closure.

components/sync/engine/fake_sync_engine.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 COMPONENTS_SYNC_ENGINE_FAKE_SYNC_ENGINE_H_
 #define COMPONENTS_SYNC_ENGINE_FAKE_SYNC_ENGINE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 64 matching lines @@
   void FlushDirectory() const override;
 
   void RequestBufferedProtocolEventsAndEnableForwarding() override;
   void DisableProtocolEventForwarding() override;
 
   void EnableDirectoryTypeDebugInfoForwarding() override;
   void DisableDirectoryTypeDebugInfoForwarding() override;
 
   void RefreshTypesForTest(ModelTypeSet types) override;
 
-  void ClearServerData(
-      const SyncManager::ClearServerDataCallback& callback) override;
+  void ClearServerData(const base::Closure& callback) override;
 
   void OnCookieJarChanged(bool account_mismatch,
                           bool empty_jar,
                           const base::Closure& callback) override;
 
   void set_fail_initial_download(bool should_fail);
 
  private:
   bool fail_initial_download_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_FAKE_SYNC_ENGINE_H_