[Sync] Convert sync to a static library.

components/sync/syncable/transaction_observer.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_SYNCABLE_TRANSACTION_OBSERVER_H_
 #define COMPONENTS_SYNC_SYNCABLE_TRANSACTION_OBSERVER_H_
 
 #include "components/sync/base/model_type.h"
-#include "components/sync/base/sync_export.h"
 #include "components/sync/syncable/write_transaction_info.h"
 
 namespace syncer {
 namespace syncable {
 
-class SYNC_EXPORT TransactionObserver {
+class TransactionObserver {
  public:
   virtual void OnTransactionWrite(
       const ImmutableWriteTransactionInfo& write_transaction_info,
       ModelTypeSet models_with_changes) = 0;
 
  protected:
   virtual ~TransactionObserver() {}
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_SYNCABLE_TRANSACTION_OBSERVER_H_