[Sync] Convert sync to a static library.

components/sync/syncable/syncable_read_transaction.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_SYNCABLE_READ_TRANSACTION_H_
 #define COMPONENTS_SYNC_SYNCABLE_SYNCABLE_READ_TRANSACTION_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
-#include "components/sync/base/sync_export.h"
 #include "components/sync/syncable/syncable_base_transaction.h"
 
 namespace syncer {
 class ReadTransaction;
 namespace syncable {
 
 // Locks db in constructor, unlocks in destructor.
-class SYNC_EXPORT ReadTransaction : public BaseTransaction {
+class ReadTransaction : public BaseTransaction {
  public:
   ReadTransaction(const tracked_objects::Location& from_here,
                   Directory* directory);
 
   ~ReadTransaction() override;
 
  protected:  // Don't allow creation on heap, except by sync API wrapper.
   void* operator new(size_t size) { return (::operator new)(size); }
 
  private:
   friend class syncer::ReadTransaction;
 
   DISALLOW_COPY_AND_ASSIGN(ReadTransaction);
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_SYNCABLE_SYNCABLE_READ_TRANSACTION_H_