Remove #pragma once from sync

sync/engine/sync_engine_event.h

 // Copyright (c) 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 SYNC_ENGINE_SYNC_ENGINE_EVENT_H_
 #define SYNC_ENGINE_SYNC_ENGINE_EVENT_H_
-#pragma once
 
 #include <string>
 
 #include "base/observer_list.h"
 #include "sync/internal_api/public/sessions/sync_session_snapshot.h"
 
 namespace syncable {
 class Id;
 }
 
@@ skipping 45 matching lines @@
   // TODO(tim): Consider splitting this up to multiple callbacks, rather than
   // have to do Event e(type); OnSyncEngineEvent(e); at all callsites,
   virtual void OnSyncEngineEvent(const SyncEngineEvent& event) = 0;
  protected:
   virtual ~SyncEngineEventListener() {}
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_SYNC_ENGINE_EVENT_H_