Implement new invalidations ack tracking system

sync/notifier/invalidation_handler.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 SYNC_NOTIFIER_INVALIDATION_HANDLER_H_
 #define SYNC_NOTIFIER_INVALIDATION_HANDLER_H_
 
 #include "sync/base/sync_export.h"
 #include "sync/notifier/invalidator_state.h"
-#include "sync/notifier/object_id_invalidation_map.h"
 
 namespace syncer {
 
+class ObjectIdInvalidationMap;
+
 class SYNC_EXPORT InvalidationHandler {
  public:
   // Called when the invalidator state changes.
   virtual void OnInvalidatorStateChange(InvalidatorState state) = 0;
 
   // Called when a invalidation is received.  The per-id states are in
   // |id_state_map| and the source is in |source|.  Note that this may be
   // called regardless of the current invalidator state.
   virtual void OnIncomingInvalidation(
       const ObjectIdInvalidationMap& invalidation_map) = 0;
 
  protected:
   virtual ~InvalidationHandler() {}
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_NOTIFIER_INVALIDATION_HANDLER_H_