Remove #pragma once from sync

sync/engine/nudge_source.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_NUDGE_SOURCE_H_
 #define SYNC_ENGINE_NUDGE_SOURCE_H_
-#pragma once
 
 namespace syncer {
 
 enum NudgeSource {
   NUDGE_SOURCE_UNKNOWN = 0,
   // We received an invalidation message and are nudging to check for updates.
   NUDGE_SOURCE_NOTIFICATION,
   // A local change occurred (e.g. bookmark moved).
   NUDGE_SOURCE_LOCAL,
   // A previous sync cycle did not fully complete (e.g. HTTP error).
   NUDGE_SOURCE_CONTINUATION,
   // A local event is triggering an optimistic datatype refresh.
   NUDGE_SOURCE_LOCAL_REFRESH,
 };
 
 const char* GetNudgeSourceString(NudgeSource nudge_source);
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_NUDGE_SOURCE_H_