[Sync] Add sync_export.h (Step 1 for componentizing sync)

sync/internal_api/public/engine/passive_model_worker.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_INTERNAL_API_PUBLIC_ENGINE_PASSIVE_MODEL_WORKER_H_
 #define SYNC_INTERNAL_API_PUBLIC_ENGINE_PASSIVE_MODEL_WORKER_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "sync/base/sync_export.h"
 #include "sync/internal_api/public/engine/model_safe_worker.h"
 #include "sync/internal_api/public/util/syncer_error.h"
 
 class MessageLoop;
 
 namespace syncer {
 
 // Implementation of ModelSafeWorker for passive types.  All work is
 // done on the same thread DoWorkAndWaitUntilDone (i.e., the sync
 // thread).
-class PassiveModelWorker : public ModelSafeWorker {
+class SYNC_EXPORT PassiveModelWorker : public ModelSafeWorker {
  public:
   explicit PassiveModelWorker(const MessageLoop* sync_loop);
 
   // ModelSafeWorker implementation. Called on the sync thread.
   virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
  private:
   virtual ~PassiveModelWorker();
 
   const MessageLoop* const sync_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(PassiveModelWorker);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_ENGINE_PASSIVE_MODEL_WORKER_H_