[Sync] Replace ClearServerDataCallback with Closure.

components/sync/engine/sync_engine.h

 // Copyright 2012 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_SYNC_ENGINE_H_
 #define COMPONENTS_SYNC_ENGINE_SYNC_ENGINE_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 163 matching lines @@
   // for all counters be emitted.
   virtual void EnableDirectoryTypeDebugInfoForwarding() = 0;
 
   // Disables the sending of directory type debug counters.
   virtual void DisableDirectoryTypeDebugInfoForwarding() = 0;
 
   // Triggers sync cycle to update |types|.
   virtual void RefreshTypesForTest(ModelTypeSet types) = 0;
 
   // See SyncManager::ClearServerData.
-  virtual void ClearServerData(
-      const SyncManager::ClearServerDataCallback& callback) = 0;
+  virtual void ClearServerData(const base::Closure& callback) = 0;
 
   // Notify the syncer that the cookie jar has changed.
   // See SyncManager::OnCookieJarChanged.
   virtual void OnCookieJarChanged(bool account_mismatch,
                                   bool empty_jar,
                                   const base::Closure& callback) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SyncEngine);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_SYNC_ENGINE_H_