[Sync] Convert sync to a static library.

components/sync/base/cancelation_observer.h

 // Copyright 2013 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_BASE_CANCELATION_OBSERVER_H_
 #define COMPONENTS_SYNC_BASE_CANCELATION_OBSERVER_H_
 
-#include "components/sync/base/sync_export.h"
-
 namespace syncer {
 
 // Interface for classes that handle signals from the CancelationSignal.
-class SYNC_EXPORT CancelationObserver {
+class CancelationObserver {
  public:
   CancelationObserver();
   virtual ~CancelationObserver() = 0;
 
   // This may be called from a foreign thread while the CancelationSignal's lock
   // is held.  The callee should avoid performing slow or blocking operations.
   virtual void OnSignalReceived() = 0;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_BASE_CANCELATION_OBSERVER_H_